/* ==========================================================================
   油耗计算器 · 全站样式
   设计语言：蓝色 #3d95fa、浅灰蓝底、胶囊按钮、8px 卡片、深色页脚
   ========================================================================== */

:root {
  --primary: #3d95fa;
  --primary-strong: #1f6fd0;
  --primary-deep: #2f66a9;
  --primary-soft: #eaf4ff;
  --grad-blue: linear-gradient(100deg, #68b8ed 0%, #3d95fa 52%, #2a7adc 100%);
  --grad-bg: linear-gradient(45deg, #f2f4f8 0%, #dbe9f6 100%);
  --bg: #edeef1;
  --surface: #f8f9fb;
  --white: #ffffff;
  --text: #1b2134;
  --text-muted: #314a70;
  --text-soft: #5d6d88;
  --border: #dddddd;
  --border-light: #e8e8e8;
  --dark: #1b2134;
  --dark-2: #232c44;
  --dark-text: #ffffff;
  --dark-muted: #94a1b5;
  --success: #167a5b;
  --warn: #9a5b00;
  --danger: #b42318;
  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-pill: 50px;
  --shadow-sm: 0 1px 2px rgba(27, 33, 52, 0.05);
  --shadow-card: 0 2px 4px rgba(27, 33, 52, 0.04), 0 22px 44px -34px rgba(27, 33, 52, 0.35);
  --shadow-tool: 0 2px 0 rgba(255, 255, 255, 0.8) inset, 0 34px 74px -38px rgba(27, 33, 52, 0.48);
  --container: 1280px;
  --narrow: 820px;
  --font-sans: "Noto Sans SC", "Source Han Sans SC", "PingFang SC", "Hiragino Sans GB",
    "Microsoft YaHei", sans-serif;
  --font-num: "Poppins", "Noto Sans SC", "PingFang SC", "Microsoft YaHei", sans-serif;
  --ease: cubic-bezier(0.25, 1, 0.5, 1);
  --header-h: 80px;
}

*,
*::before,
*::after {
  box-sizing: border-box;
}

html {
  -webkit-text-size-adjust: 100%;
  scroll-behavior: smooth;
  scroll-padding-top: calc(var(--header-h) + 20px);
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--font-sans);
  font-size: 17px;
  font-weight: 400;
  line-height: 1.75;
  text-rendering: optimizeLegibility;
  -webkit-font-smoothing: antialiased;
}

body.nav-open {
  overflow: hidden;
}

h1,
h2,
h3,
h4,
p,
ul,
ol,
figure,
blockquote {
  margin: 0;
}

ul,
ol {
  padding: 0;
  list-style: none;
}

img,
svg {
  display: block;
  max-width: 100%;
}

a {
  color: var(--primary-strong);
  text-decoration: none;
}

button,
input,
select,
textarea {
  font: inherit;
  color: inherit;
}

button {
  cursor: pointer;
}

::selection {
  background: rgba(61, 149, 250, 0.22);
  color: var(--text);
}

:focus-visible {
  outline: 2px solid var(--primary-strong);
  outline-offset: 3px;
}

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

.skip-link {
  position: fixed;
  top: 10px;
  left: 10px;
  z-index: 200;
  padding: 10px 18px;
  border-radius: var(--radius-sm);
  background: var(--dark);
  color: #fff;
  transform: translateY(-160%);
  transition: transform 0.2s var(--ease);
}

.skip-link:focus {
  transform: translateY(0);
}

.container {
  width: min(calc(100% - 80px), var(--container));
  margin-inline: auto;
}

.container--narrow {
  width: min(calc(100% - 80px), var(--narrow));
}

/* --------------------------------------------------------------------------
   页头
   -------------------------------------------------------------------------- */

.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(255, 255, 255, 0.94);
  border-bottom: 1px solid rgba(221, 221, 221, 0.7);
  backdrop-filter: blur(14px);
  transition: box-shadow 0.3s var(--ease);
}

.site-header.is-scrolled {
  box-shadow: 0 1px 4px rgba(27, 33, 52, 0.08);
}

.header-inner {
  width: min(calc(100% - 80px), var(--container));
  min-height: var(--header-h);
  margin-inline: auto;
  display: flex;
  align-items: center;
  gap: 32px;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 12px;
  color: var(--text);
  flex: 0 0 auto;
}

.brand-mark {
  width: 42px;
  height: 42px;
  flex: 0 0 42px;
  filter: drop-shadow(0 4px 8px rgba(61, 149, 250, 0.24));
}

.brand-mark svg {
  width: 100%;
  height: 100%;
}

.brand-text {
  display: flex;
  flex-direction: column;
  line-height: 1.15;
}

.brand-text strong {
  font-size: 19px;
  font-weight: 700;
  letter-spacing: 0.01em;
}

.brand-text small {
  margin-top: 4px;
  color: var(--primary-deep);
  font-family: var(--font-num);
  font-size: 9px;
  font-weight: 600;
  letter-spacing: 0.18em;
}

.site-nav {
  margin-left: auto;
}

.site-nav ul {
  display: flex;
  align-items: center;
  gap: 27px;
}

.nav-link {
  position: relative;
  display: inline-block;
  padding: 27px 0 25px;
  color: var(--text);
  font-size: 15px;
  font-weight: 500;
  white-space: nowrap;
  transition: color 0.3s ease-out;
}

.nav-link::after {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  bottom: 17px;
  height: 2px;
  background: var(--primary);
  transform: scaleX(0);
  transform-origin: left;
  transition: transform 0.3s var(--ease);
}

.nav-link:hover,
.nav-link.is-active {
  color: var(--primary-strong);
}

.nav-link:hover::after,
.nav-link.is-active::after {
  transform: scaleX(1);
}

.nav-toggle {
  display: none;
  width: 44px;
  height: 44px;
  margin-left: auto;
  padding: 11px;
  border: 1px solid var(--border-light);
  border-radius: var(--radius-sm);
  background: var(--white);
}

.nav-toggle span {
  display: block;
  height: 2px;
  margin: 5px 0;
  border-radius: 2px;
  background: var(--text);
  transition: transform 0.3s var(--ease), opacity 0.2s linear;
}

.nav-toggle[aria-expanded="true"] span:nth-child(1) {
  transform: translateY(7px) rotate(45deg);
}

.nav-toggle[aria-expanded="true"] span:nth-child(2) {
  opacity: 0;
}

.nav-toggle[aria-expanded="true"] span:nth-child(3) {
  transform: translateY(-7px) rotate(-45deg);
}

/* --------------------------------------------------------------------------
   首页 Hero
   -------------------------------------------------------------------------- */

.hero {
  position: relative;
  isolation: isolate;
  overflow: hidden;
  padding: 66px 0 88px;
  background: var(--grad-bg);
}

.hero::before {
  content: "";
  position: absolute;
  inset: 0;
  z-index: -2;
  background:
    radial-gradient(620px 360px at 82% 8%, rgba(61, 149, 250, 0.2), transparent 68%),
    radial-gradient(480px 300px at 10% 44%, rgba(255, 255, 255, 0.85), transparent 70%),
    radial-gradient(rgba(47, 102, 169, 0.11) 1px, transparent 1px);
  background-size: auto, auto, 22px 22px;
  mask-image: linear-gradient(to bottom, #000 0%, rgba(0, 0, 0, 0.65) 62%, transparent 100%);
  -webkit-mask-image: linear-gradient(to bottom, #000 0%, rgba(0, 0, 0, 0.65) 62%, transparent 100%);
}

.hero-deco {
  position: absolute;
  z-index: -1;
  top: 34px;
  right: max(-180px, calc(50% - 900px));
  width: 560px;
  color: var(--primary);
  opacity: 0.22;
  pointer-events: none;
}

.hero-deco svg {
  width: 100%;
  height: auto;
}

.hero-inner {
  width: min(calc(100% - 80px), 1080px);
  margin-inline: auto;
  text-align: center;
}

.hero h1 {
  max-width: 900px;
  margin-inline: auto;
  color: var(--text);
  font-size: clamp(42px, 5.6vw, 69px);
  font-weight: 700;
  line-height: 1.14;
  letter-spacing: -0.035em;
  background: linear-gradient(108deg, #2f66a9 0%, #1b2134 68%);
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
  animation: rise 0.7s var(--ease) both;
}

.hero-lead {
  max-width: 760px;
  margin: 20px auto 38px;
  color: var(--text-muted);
  font-size: 18px;
  line-height: 1.8;
  animation: rise 0.7s 0.08s var(--ease) both;
}

.hero .calc-shell {
  text-align: left;
  animation: rise 0.75s 0.16s var(--ease) both;
}

@keyframes rise {
  from {
    opacity: 0;
    transform: translateY(20px);
  }
  to {
    opacity: 1;
    transform: none;
  }
}

/* --------------------------------------------------------------------------
   计算器
   -------------------------------------------------------------------------- */

.calc-card {
  position: relative;
  overflow: hidden;
  padding: clamp(22px, 3.2vw, 36px);
  border-radius: var(--radius-md);
  background: var(--white);
  box-shadow: var(--shadow-tool);
}

.calc-card::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 4px;
  background: var(--grad-blue);
}

.calc-head {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 20px;
  padding-bottom: 20px;
  border-bottom: 1px solid var(--border-light);
}

.calc-kicker {
  margin-bottom: 4px;
  color: var(--primary-deep);
  font-family: var(--font-num);
  font-size: 10px;
  font-weight: 600;
  letter-spacing: 0.16em;
  text-transform: uppercase;
}

.calc-head h2 {
  font-size: 22px;
  font-weight: 700;
  line-height: 1.35;
  letter-spacing: -0.01em;
}

.calc-sample {
  margin-top: 5px;
  color: var(--text-soft);
  font-size: 12px;
  line-height: 1.6;
}

.calc-badge {
  flex: 0 0 auto;
  margin-top: 3px;
  padding: 6px 13px;
  border: 1px solid #cfe6fb;
  border-radius: var(--radius-pill);
  background: var(--primary-soft);
  color: var(--primary-deep);
  font-size: 12px;
  font-weight: 600;
  white-space: nowrap;
}

.calc-tabs {
  display: inline-flex;
  gap: 4px;
  margin: 22px 0 24px;
  padding: 4px;
  border-radius: var(--radius-pill);
  background: #f0f3f7;
}

.calc-tab {
  min-height: 44px;
  padding: 0 20px;
  border: 0;
  border-radius: var(--radius-pill);
  background: transparent;
  color: var(--text-muted);
  font-size: 14px;
  font-weight: 600;
  transition: background 0.3s ease-out, color 0.3s ease-out, box-shadow 0.3s ease-out;
}

.calc-tab.is-active {
  background: var(--white);
  color: var(--primary-strong);
  box-shadow: 0 1px 4px rgba(27, 33, 52, 0.12);
}

.calc-panel[hidden] {
  display: none;
}

.calc-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 20px;
}

.calc-grid--two {
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.field {
  min-width: 0;
}

.field label {
  display: block;
  margin-bottom: 8px;
  color: var(--text);
  font-size: 15px;
  font-weight: 600;
}

.field label .optional {
  margin-left: 5px;
  color: var(--text-soft);
  font-size: 12px;
  font-weight: 400;
}

.input-wrap {
  position: relative;
}

.input-wrap input {
  width: 100%;
  height: 56px;
  padding: 0 78px 0 16px;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  background: var(--white);
  color: var(--text);
  font-family: var(--font-num);
  font-size: 19px;
  font-weight: 500;
  font-variant-numeric: tabular-nums;
  transition: border-color 0.3s ease-out, box-shadow 0.3s ease-out;
}

.input-wrap input::placeholder {
  color: #8b98ad;
  font-weight: 400;
}

.input-wrap input:focus {
  border-color: var(--primary);
  outline: none;
  box-shadow: 0 0 0 3px rgba(61, 149, 250, 0.2);
}

.input-wrap input:invalid {
  box-shadow: none;
}

.input-wrap .unit {
  position: absolute;
  top: 50%;
  right: 15px;
  transform: translateY(-50%);
  color: var(--text-soft);
  font-family: var(--font-num);
  font-size: 13px;
  font-weight: 500;
  pointer-events: none;
}

.field-hint {
  margin-top: 7px;
  color: var(--text-soft);
  font-size: 12.5px;
  line-height: 1.55;
}

.calc-actions {
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  gap: 10px;
  margin-top: 22px;
}

.calc-error {
  margin-top: 14px;
  padding: 10px 14px;
  border-left: 3px solid var(--danger);
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  background: #fdf2f0;
  color: #8f1d14;
  font-size: 14px;
}

.calc-results {
  display: grid;
  grid-template-columns: minmax(0, 1.08fr) minmax(0, 1fr);
  gap: 14px;
  margin-top: 26px;
}

.result-main {
  position: relative;
  display: flex;
  flex-direction: column;
  justify-content: center;
  min-height: 188px;
  padding: 26px 28px;
  overflow: hidden;
  border-radius: var(--radius-md);
  background: var(--dark);
  color: var(--dark-text);
}

.result-main::after {
  content: "";
  position: absolute;
  right: -48px;
  bottom: -72px;
  width: 240px;
  height: 240px;
  border-radius: 50%;
  background: radial-gradient(circle, rgba(61, 149, 250, 0.55), transparent 66%);
  pointer-events: none;
}

.result-label {
  position: relative;
  z-index: 1;
  color: #c6d4e8;
  font-size: 13px;
  font-weight: 500;
  letter-spacing: 0.04em;
}

.result-number {
  position: relative;
  z-index: 1;
  display: flex;
  align-items: baseline;
  flex-wrap: wrap;
  gap: 10px;
  margin: 8px 0 6px;
  color: #fff;
  font-family: var(--font-num);
  font-size: clamp(46px, 6vw, 62px);
  font-weight: 600;
  line-height: 1;
  letter-spacing: -0.04em;
  font-variant-numeric: tabular-nums;
}

.result-unit {
  color: #8fc4f7;
  font-size: 16px;
  font-weight: 500;
  letter-spacing: 0;
}

.result-foot {
  position: relative;
  z-index: 1;
  color: var(--dark-muted);
  font-size: 12.5px;
  line-height: 1.6;
}

.result-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 10px;
}

.result-item {
  display: flex;
  flex-direction: column;
  justify-content: center;
  min-height: 88px;
  padding: 14px 16px;
  border: 1px solid var(--border-light);
  border-radius: var(--radius-md);
  background: var(--surface);
}

.result-item span {
  color: var(--text-soft);
  font-size: 12px;
  line-height: 1.4;
}

.result-item strong {
  margin-top: 5px;
  color: var(--text);
  font-family: var(--font-num);
  font-size: 21px;
  font-weight: 600;
  line-height: 1.15;
  font-variant-numeric: tabular-nums;
}

.calc-footnote {
  margin-top: 16px;
  color: var(--text-soft);
  font-size: 12px;
  line-height: 1.65;
}

.calc-intro-note {
  display: flex;
  gap: 10px;
  margin-top: 18px;
  padding: 12px 16px;
  border-radius: var(--radius-sm);
  background: var(--surface);
  color: var(--text-muted);
  font-size: 13.5px;
}

.calc-intro-note svg {
  width: 18px;
  height: 18px;
  flex: 0 0 18px;
  margin-top: 2px;
  color: var(--primary-strong);
}

/* 工具页 */
.calc-section {
  padding: 34px 0 80px;
  background: var(--grad-bg);
}

.calc-shell--wide {
  width: min(calc(100% - 80px), 1120px);
  margin-inline: auto;
}

/* 小工具：单位换算 */
.convert-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 24px;
}

.convert-card {
  padding: 28px;
  border: 1px solid var(--border-light);
  border-radius: var(--radius-md);
  background: var(--white);
  box-shadow: var(--shadow-sm);
}

.convert-card h3 {
  margin-bottom: 6px;
  font-size: 19px;
}

.convert-card > p {
  margin-bottom: 18px;
  color: var(--text-soft);
  font-size: 14px;
}

.convert-input {
  display: flex;
  gap: 10px;
}

.convert-input input {
  min-width: 0;
  flex: 1;
  height: 50px;
  padding: 0 14px;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  font-family: var(--font-num);
  font-size: 18px;
}

.convert-input input:focus {
  border-color: var(--primary);
  outline: none;
  box-shadow: 0 0 0 3px rgba(61, 149, 250, 0.2);
}

.convert-out {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 8px;
  margin-top: 16px;
}

.convert-out div {
  padding: 12px;
  border-radius: var(--radius-sm);
  background: var(--surface);
}

.convert-out span {
  display: block;
  color: var(--text-soft);
  font-size: 11px;
}

.convert-out strong {
  display: block;
  margin-top: 2px;
  font-family: var(--font-num);
  font-size: 18px;
  font-variant-numeric: tabular-nums;
}

.convert-out--two {
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

/* --------------------------------------------------------------------------
   内页 Hero
   -------------------------------------------------------------------------- */

.page-hero {
  position: relative;
  overflow: hidden;
  padding: 34px 0 58px;
  background:
    radial-gradient(700px 300px at 88% 0%, rgba(61, 149, 250, 0.16), transparent 70%),
    linear-gradient(180deg, #f4f7fa 0%, #e6eef7 100%);
  border-bottom: 1px solid rgba(221, 221, 221, 0.8);
}

.page-hero::after {
  content: "";
  position: absolute;
  right: -120px;
  top: -90px;
  width: 380px;
  height: 380px;
  border: 1px solid rgba(61, 149, 250, 0.18);
  border-radius: 50%;
  box-shadow: 0 0 0 38px rgba(61, 149, 250, 0.04), 0 0 0 76px rgba(61, 149, 250, 0.03);
  pointer-events: none;
}

.page-hero .container {
  position: relative;
  z-index: 1;
}

.breadcrumb {
  margin-bottom: 26px;
}

.breadcrumb ol {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 6px;
  color: var(--text-soft);
  font-size: 12.5px;
}

.breadcrumb li {
  display: inline-flex;
  align-items: center;
  gap: 6px;
}

.breadcrumb li + li::before {
  content: "/";
  color: #a9b4c5;
}

.breadcrumb a {
  color: var(--text-muted);
}

.breadcrumb a:hover {
  color: var(--primary-strong);
}

.page-hero h1 {
  max-width: 900px;
  font-size: clamp(34px, 4.5vw, 50px);
  font-weight: 700;
  line-height: 1.2;
  letter-spacing: -0.025em;
}

.page-lead {
  max-width: 760px;
  margin-top: 16px;
  color: var(--text-muted);
  font-size: 17.5px;
  line-height: 1.85;
}

.eyebrow {
  display: inline-flex;
  align-items: center;
  gap: 9px;
  margin-bottom: 12px;
  color: var(--primary-deep);
  font-family: var(--font-num);
  font-size: 10.5px;
  font-weight: 600;
  letter-spacing: 0.17em;
  text-transform: uppercase;
}

.eyebrow::before {
  content: "";
  width: 20px;
  height: 2px;
  background: currentColor;
}

.eyebrow--light {
  color: #d8ecff;
}

/* --------------------------------------------------------------------------
   通用区块
   -------------------------------------------------------------------------- */

.section {
  padding: 80px 0;
}

.section--tight {
  padding: 64px 0;
}

.section--white {
  background: var(--white);
}

.section--surface {
  background: var(--surface);
}

.section--gradient {
  background: linear-gradient(180deg, #f2f4f8 0%, #e6eef7 100%);
}

.section--border-top {
  border-top: 1px solid var(--border-light);
}

.section-head {
  max-width: 800px;
  margin-bottom: 42px;
}

.section-head--center {
  margin-inline: auto;
  text-align: center;
}

.section-head--center .eyebrow {
  justify-content: center;
}

.section-head h2 {
  font-size: clamp(28px, 3.5vw, 43px);
  font-weight: 700;
  line-height: 1.2;
  letter-spacing: -0.025em;
}

.section-head .section-lead {
  margin-top: 16px;
  color: var(--text-muted);
  font-size: 17px;
  line-height: 1.85;
}

.section-head .section-lead + .section-lead {
  margin-top: 10px;
}

.grid {
  display: grid;
  gap: 20px;
}

.grid--2 {
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.grid--3 {
  grid-template-columns: repeat(3, minmax(0, 1fr));
}

.grid--4 {
  grid-template-columns: repeat(4, minmax(0, 1fr));
}

.grid--gap-lg {
  gap: 28px;
}

.u-mt-20 {
  margin-top: 20px;
}

.u-mt-28 {
  margin-top: 28px;
}

.u-mt-32 {
  margin-top: 32px;
}

.u-mt-40 {
  margin-top: 40px;
}

.u-mb-0 {
  margin-bottom: 0;
}

.card {
  display: flex;
  flex-direction: column;
  padding: 28px;
  border: 1px solid rgba(232, 232, 232, 0.9);
  border-radius: var(--radius-md);
  background: var(--white);
  box-shadow: var(--shadow-sm);
  transition: transform 0.3s var(--ease), box-shadow 0.3s var(--ease), border-color 0.3s ease-out;
}

.card:hover {
  transform: translateY(-3px);
  border-color: #d6e6f7;
  box-shadow: 0 4px 12px rgba(27, 33, 52, 0.08);
}

.card h3 {
  margin-bottom: 8px;
  color: var(--text);
  font-size: 19px;
  font-weight: 700;
  line-height: 1.45;
  letter-spacing: -0.01em;
}

.card p {
  color: var(--text-muted);
  font-size: 15px;
  line-height: 1.8;
}

.card p + p {
  margin-top: 10px;
}

.card-link {
  display: inline-flex;
  align-items: center;
  gap: 7px;
  color: var(--primary-strong);
  font-size: 14px;
  font-weight: 600;
}

.card-link svg {
  width: 16px;
  height: 16px;
  transition: transform 0.3s var(--ease);
}

.card-link:hover {
  color: var(--primary-deep);
}

.card-link:hover svg {
  transform: translateX(4px);
}

.card .card-link {
  margin-top: auto;
  padding-top: 18px;
}

.card-icon {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 46px;
  height: 46px;
  margin-bottom: 18px;
  border-radius: 50%;
  background: var(--primary-soft);
  color: var(--primary-strong);
}

.card-icon svg {
  width: 23px;
  height: 23px;
}

.card-icon--dark {
  background: rgba(255, 255, 255, 0.09);
  color: #9ed0ff;
}

.card--dark {
  border-color: rgba(255, 255, 255, 0.08);
  background: var(--dark-2);
  box-shadow: none;
}

.card--dark h3 {
  color: #fff;
}

.card--dark p {
  color: #b8c5d9;
}

.card--dark:hover {
  border-color: rgba(104, 184, 237, 0.4);
  box-shadow: 0 16px 34px -24px rgba(0, 0, 0, 0.5);
}

/* --------------------------------------------------------------------------
   公式与示例
   -------------------------------------------------------------------------- */

.formula-box {
  position: relative;
  display: grid;
  grid-template-columns: minmax(0, 1.25fr) minmax(0, 0.75fr);
  gap: 34px;
  overflow: hidden;
  padding: clamp(28px, 4vw, 44px);
  border-radius: var(--radius-md);
  background: linear-gradient(135deg, #1b2134 0%, #25324f 100%);
  color: #fff;
  box-shadow: 0 26px 60px -38px rgba(27, 33, 52, 0.7);
}

.formula-box::before {
  content: "";
  position: absolute;
  top: -130px;
  right: -80px;
  width: 360px;
  height: 360px;
  border-radius: 50%;
  background: radial-gradient(circle, rgba(61, 149, 250, 0.3), transparent 65%);
  pointer-events: none;
}

.formula-label {
  color: #9ed0ff;
  font-family: var(--font-num);
  font-size: 10.5px;
  font-weight: 600;
  letter-spacing: 0.17em;
  text-transform: uppercase;
}

.formula-equation {
  margin: 14px 0 16px;
  color: #fff;
  font-size: clamp(20px, 2.2vw, 26px);
  font-weight: 600;
  line-height: 1.55;
  letter-spacing: -0.015em;
}

.formula-equation em {
  color: #8fc4f7;
  font-style: normal;
  white-space: nowrap;
}

.formula-note {
  max-width: 560px;
  color: #b9c7da;
  font-size: 14.5px;
  line-height: 1.8;
}

.formula-example {
  position: relative;
  z-index: 1;
  align-self: center;
  padding: 22px;
  border: 1px solid rgba(255, 255, 255, 0.12);
  border-radius: var(--radius-md);
  background: rgba(255, 255, 255, 0.055);
}

.formula-example p {
  color: #c6d4e8;
  font-size: 13px;
  line-height: 1.7;
}

.formula-example strong {
  display: block;
  margin: 4px 0 12px;
  color: #fff;
  font-family: var(--font-num);
  font-size: 30px;
  font-weight: 600;
  line-height: 1.2;
  font-variant-numeric: tabular-nums;
}

.formula-example strong span {
  margin-left: 4px;
  color: #8fc4f7;
  font-size: 13px;
  font-weight: 500;
}

.formula-example p:last-child {
  margin-top: 10px;
  padding-top: 10px;
  border-top: 1px solid rgba(255, 255, 255, 0.12);
}

/* 步骤 */
.steps {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 18px;
  counter-reset: step;
}

.step {
  position: relative;
  padding: 26px 24px;
  border: 1px solid var(--border-light);
  border-radius: var(--radius-md);
  background: var(--white);
}

.step-num {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 38px;
  height: 38px;
  margin-bottom: 16px;
  border-radius: 50%;
  background: var(--grad-blue);
  color: #fff;
  font-family: var(--font-num);
  font-size: 14px;
  font-weight: 600;
  box-shadow: 0 8px 16px -8px rgba(61, 149, 250, 0.7);
}

.step h3 {
  margin-bottom: 8px;
  font-size: 17px;
  line-height: 1.45;
}

.step p {
  color: var(--text-muted);
  font-size: 14px;
  line-height: 1.8;
}

/* 提示框 */
.note {
  padding: 18px 22px;
  border-left: 3px solid var(--primary);
  border-radius: 0 var(--radius-md) var(--radius-md) 0;
  background: var(--surface);
  color: var(--text-muted);
  font-size: 14.5px;
  line-height: 1.8;
}

.note strong {
  color: var(--text);
}

.note--tip {
  border-left-color: #1a8a66;
  background: #f0faf6;
}

.note--warn {
  border-left-color: #c77c00;
  background: #fff8ec;
}

.note + .note {
  margin-top: 12px;
}

/* --------------------------------------------------------------------------
   表格
   -------------------------------------------------------------------------- */

.grid > *,
.split > *,
.article-grid > *,
.quick-facts > *,
.steps > * {
  min-width: 0;
}

.table-wrap {
  min-width: 0;
  max-width: 100%;
  overflow-x: auto;
  scrollbar-width: thin;
  scrollbar-color: #c5d4e5 transparent;
  border: 1px solid var(--border-light);
  border-radius: var(--radius-md);
  background: var(--white);
  -webkit-overflow-scrolling: touch;
}

table {
  width: 100%;
  min-width: 560px;
  border-collapse: collapse;
  font-size: 14.5px;
}

caption {
  padding: 16px 18px 0;
  color: var(--text-soft);
  font-size: 12.5px;
  text-align: left;
}

th,
td {
  padding: 14px 18px;
  border-bottom: 1px solid var(--border-light);
  text-align: left;
  vertical-align: middle;
}

thead th {
  background: var(--surface);
  color: var(--text);
  font-size: 13px;
  font-weight: 600;
  white-space: nowrap;
}

tbody tr:last-child td {
  border-bottom: 0;
}

tbody tr:hover td {
  background: #fbfdff;
}

td strong {
  font-weight: 600;
}

.num {
  font-family: var(--font-num);
  font-variant-numeric: tabular-nums;
  white-space: nowrap;
}

.table-scroll-hint {
  margin-top: 8px;
  color: var(--text-soft);
  font-size: 11.5px;
  line-height: 1.6;
  text-align: right;
}

.table-wrap.is-scrollable:focus-visible {
  outline: 2px solid var(--primary-strong);
  outline-offset: 3px;
}

.table-note {
  margin-top: 12px;
  color: var(--text-soft);
  font-size: 12.5px;
  line-height: 1.7;
}

/* --------------------------------------------------------------------------
   清单
   -------------------------------------------------------------------------- */

.checklist {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 12px;
}

.checklist li {
  position: relative;
  padding: 16px 20px 16px 48px;
  border: 1px solid var(--border-light);
  border-radius: var(--radius-md);
  background: var(--white);
  color: var(--text-muted);
  font-size: 14.5px;
  line-height: 1.75;
}

.checklist li::before {
  content: "";
  position: absolute;
  left: 18px;
  top: 21px;
  width: 16px;
  height: 9px;
  border-left: 2px solid #1a8a66;
  border-bottom: 2px solid #1a8a66;
  transform: rotate(-45deg);
}

.checklist strong {
  display: block;
  color: var(--text);
  font-weight: 600;
}

/* --------------------------------------------------------------------------
   FAQ
   -------------------------------------------------------------------------- */

.faq-list {
  border-top: 1px solid var(--border);
}

.faq-item {
  border-bottom: 1px solid var(--border);
}

.faq-item summary {
  position: relative;
  padding: 21px 54px 21px 0;
  color: var(--text);
  font-size: 16.5px;
  font-weight: 600;
  line-height: 1.6;
  cursor: pointer;
  list-style: none;
}

.faq-item summary::-webkit-details-marker {
  display: none;
}

.faq-item summary::before,
.faq-item summary::after {
  content: "";
  position: absolute;
  right: 12px;
  top: 50%;
  width: 13px;
  height: 2px;
  border-radius: 2px;
  background: var(--primary-strong);
  transition: transform 0.3s var(--ease);
}

.faq-item summary::after {
  transform: rotate(90deg);
}

.faq-item[open] summary::after {
  transform: rotate(0);
}

.faq-item summary:hover {
  color: var(--primary-strong);
}

.faq-answer {
  max-width: 880px;
  padding: 0 54px 22px 0;
  color: var(--text-muted);
  font-size: 15px;
  line-height: 1.9;
}

.faq-answer p + p {
  margin-top: 10px;
}

.faq-answer a {
  text-decoration: underline;
  text-underline-offset: 3px;
}

.faq-group + .faq-group {
  margin-top: 58px;
}

.faq-more {
  margin-top: 26px;
  color: var(--text-muted);
  font-size: 14.5px;
}

/* --------------------------------------------------------------------------
   文章卡片
   -------------------------------------------------------------------------- */

.article-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 22px;
}

.article-card {
  display: flex;
  flex-direction: column;
  padding: 26px;
  border: 1px solid var(--border-light);
  border-radius: var(--radius-md);
  background: var(--white);
  transition: transform 0.3s var(--ease), box-shadow 0.3s var(--ease);
}

.article-card:hover {
  transform: translateY(-3px);
  box-shadow: 0 16px 34px -28px rgba(27, 33, 52, 0.45);
}

.article-card-tag {
  display: inline-flex;
  align-self: flex-start;
  margin-bottom: 14px;
  padding: 4px 10px;
  border-radius: 3px;
  background: var(--primary-soft);
  color: var(--primary-deep);
  font-size: 11.5px;
  font-weight: 600;
}

.article-card h3 {
  margin-bottom: 9px;
  font-size: 20px;
  font-weight: 700;
  line-height: 1.5;
  letter-spacing: -0.01em;
}

.article-card h3 a {
  color: var(--text);
}

.article-card h3 a:hover {
  color: var(--primary-strong);
}

.article-card > p:not(.article-card-tag):not(.article-card-meta) {
  color: var(--text-muted);
  font-size: 14.5px;
  line-height: 1.8;
}

.article-card-meta {
  display: flex;
  align-items: center;
  gap: 8px;
  margin-top: auto;
  padding-top: 20px;
  color: var(--text-soft);
  font-size: 12px;
}

/* 相关链接 */
.related-links {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 12px;
}

.related-link {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 18px;
  padding: 20px 22px;
  border: 1px solid var(--border-light);
  border-radius: var(--radius-md);
  background: var(--white);
  transition: border-color 0.3s ease-out, transform 0.3s var(--ease);
}

.related-link:hover {
  border-color: #cfe2f6;
  transform: translateY(-2px);
}

.related-link small {
  display: block;
  color: var(--text-soft);
  font-size: 11px;
  letter-spacing: 0.05em;
}

.related-link strong {
  display: block;
  margin-top: 3px;
  color: var(--text);
  font-size: 16px;
  font-weight: 600;
}

.related-link svg {
  width: 20px;
  height: 20px;
  flex: 0 0 20px;
  color: var(--primary-strong);
  transition: transform 0.3s var(--ease);
}

.related-link:hover svg {
  transform: translateX(4px);
}

/* --------------------------------------------------------------------------
   CTA
   -------------------------------------------------------------------------- */

.cta-band {
  position: relative;
  overflow: hidden;
  padding: 62px 0;
  background: var(--grad-blue);
  color: #fff;
}

.cta-band::before {
  content: "";
  position: absolute;
  inset: 0;
  background:
    radial-gradient(500px 260px at 15% 0%, rgba(255, 255, 255, 0.28), transparent 70%),
    radial-gradient(rgba(255, 255, 255, 0.22) 1px, transparent 1px);
  background-size: auto, 26px 26px;
  mask-image: linear-gradient(90deg, #000, transparent 70%);
  -webkit-mask-image: linear-gradient(90deg, #000, transparent 70%);
  pointer-events: none;
}

.cta-inner {
  position: relative;
  z-index: 1;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 40px;
}

.cta-inner h2 {
  max-width: 680px;
  font-size: clamp(27px, 3.4vw, 38px);
  font-weight: 700;
  line-height: 1.3;
  letter-spacing: -0.02em;
}

.cta-inner p:not(.eyebrow) {
  max-width: 620px;
  margin-top: 10px;
  color: rgba(255, 255, 255, 0.9);
  font-size: 15.5px;
  line-height: 1.8;
}

.cta-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  flex: 0 0 auto;
}

/* --------------------------------------------------------------------------
   按钮
   -------------------------------------------------------------------------- */

.button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 9px;
  min-height: 52px;
  padding: 0 28px;
  border: 1px solid transparent;
  border-radius: var(--radius-pill);
  background: transparent;
  color: var(--text);
  font-size: 15.5px;
  font-weight: 600;
  line-height: 1.2;
  text-align: center;
  white-space: nowrap;
  transition: background-color 0.3s ease-out, color 0.3s ease-out, border-color 0.3s ease-out,
    transform 0.3s var(--ease), box-shadow 0.3s ease-out;
}

.button svg {
  width: 18px;
  height: 18px;
}

.button--primary {
  background: var(--grad-blue);
  color: #fff;
  text-shadow: 0 1px 1px rgba(27, 33, 52, 0.18);
  box-shadow: 0 10px 22px -12px rgba(42, 122, 220, 0.9);
}

.button--primary:hover,
.button--primary:focus-visible {
  background: var(--primary-strong);
  color: #fff;
  transform: translateY(-1px);
  box-shadow: 0 14px 26px -12px rgba(31, 111, 208, 0.9);
}

.button--primary:active {
  transform: translateY(1px);
}

.button--secondary {
  border-color: var(--primary);
  background: var(--white);
  color: var(--primary-strong);
}

.button--secondary:hover,
.button--secondary:focus-visible {
  background: var(--primary-strong);
  border-color: var(--primary-strong);
  color: #fff;
}

.button--ghost {
  min-height: 44px;
  padding: 0 16px;
  color: var(--text-muted);
  font-size: 14px;
  font-weight: 500;
}

.button--ghost:hover,
.button--ghost:focus-visible {
  background: var(--surface);
  color: var(--primary-strong);
}

.button--white {
  background: #fff;
  color: var(--primary-deep);
  box-shadow: 0 10px 24px -14px rgba(27, 33, 52, 0.5);
}

.button--white:hover {
  background: #f4f9ff;
  transform: translateY(-1px);
}

.button--outline-light {
  border-color: rgba(255, 255, 255, 0.55);
  color: #fff;
}

.button--outline-light:hover {
  border-color: #fff;
  background: rgba(255, 255, 255, 0.12);
}

.button--sm {
  min-height: 44px;
  padding: 0 22px;
  font-size: 14px;
}

.button--block {
  width: 100%;
}

/* --------------------------------------------------------------------------
   长文排版
   -------------------------------------------------------------------------- */

.prose {
  color: var(--text-muted);
  font-size: 16.5px;
  line-height: 1.95;
}

.prose > * + * {
  margin-top: 18px;
}

.prose h2 {
  margin-top: 54px;
  color: var(--text);
  font-size: clamp(25px, 2.8vw, 32px);
  font-weight: 700;
  line-height: 1.35;
  letter-spacing: -0.02em;
  scroll-margin-top: calc(var(--header-h) + 20px);
}

.prose h2:first-child {
  margin-top: 0;
}

.prose h3 {
  margin-top: 34px;
  color: var(--text);
  font-size: 21px;
  font-weight: 700;
  line-height: 1.45;
  scroll-margin-top: calc(var(--header-h) + 20px);
}

.prose p strong,
.prose li strong {
  color: var(--text);
  font-weight: 600;
}

.prose a {
  color: var(--primary-strong);
  text-decoration: underline;
  text-decoration-thickness: 1px;
  text-underline-offset: 4px;
}

.prose a:hover {
  color: var(--primary-deep);
}

.prose ul,
.prose ol {
  padding-left: 0;
}

.prose ul li,
.prose ol li {
  position: relative;
  padding-left: 24px;
}

.prose ul li + li,
.prose ol li + li {
  margin-top: 8px;
}

.prose ul li::before {
  content: "";
  position: absolute;
  left: 4px;
  top: 13px;
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: var(--primary);
}

.prose ol {
  counter-reset: ol;
}

.prose ol li {
  counter-increment: ol;
  padding-left: 32px;
}

.prose ol li::before {
  content: counter(ol) ".";
  position: absolute;
  left: 0;
  top: 0;
  color: var(--primary-strong);
  font-family: var(--font-num);
  font-size: 14px;
  font-weight: 600;
}

.prose blockquote {
  padding: 22px 26px;
  border-left: 3px solid var(--primary);
  border-radius: 0 var(--radius-md) var(--radius-md) 0;
  background: var(--surface);
  color: var(--text-muted);
  font-size: 16px;
}

.prose blockquote p + p {
  margin-top: 10px;
}

.prose .table-wrap {
  margin-top: 26px;
}

.prose .note {
  margin-top: 26px;
}

.prose .formula-box {
  margin-top: 30px;
}

.prose .checklist {
  margin-top: 24px;
}

.prose .steps {
  margin-top: 28px;
}

.prose .convert-grid {
  margin-top: 28px;
}

/* 文章页 */
.article-hero {
  padding: 34px 0 44px;
  background:
    radial-gradient(620px 280px at 90% 0%, rgba(61, 149, 250, 0.14), transparent 70%),
    linear-gradient(180deg, #f4f7fa 0%, #e9f0f8 100%);
  border-bottom: 1px solid rgba(221, 221, 221, 0.8);
}

.article-hero h1 {
  max-width: 860px;
  font-size: clamp(31px, 4.2vw, 46px);
  font-weight: 700;
  line-height: 1.3;
  letter-spacing: -0.025em;
}

.article-meta {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 10px;
  margin-top: 18px;
  color: var(--text-soft);
  font-size: 12.5px;
}

.article-meta span[aria-hidden] {
  color: #adb8c8;
}

.article-body {
  max-width: 800px;
  margin-inline: auto;
}

.article-footer {
  max-width: 800px;
  margin: 52px auto 0;
  padding-top: 30px;
  border-top: 1px solid var(--border);
}

.author-box {
  display: flex;
  gap: 16px;
  padding: 22px;
  border: 1px solid var(--border-light);
  border-radius: var(--radius-md);
  background: var(--surface);
}

.author-box .card-icon {
  flex: 0 0 46px;
  margin: 0;
}

.author-box h2 {
  margin-bottom: 4px;
  font-size: 15px;
}

.author-box p {
  color: var(--text-muted);
  font-size: 13.5px;
  line-height: 1.75;
}

.article-nav {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 20px;
  margin-top: 22px;
  font-size: 14px;
}

.article-nav a {
  color: var(--primary-strong);
  font-weight: 600;
}

/* --------------------------------------------------------------------------
   页脚
   -------------------------------------------------------------------------- */

.site-footer {
  padding-top: 66px;
  background: var(--dark);
  color: #fff;
}

.footer-grid {
  display: grid;
  grid-template-columns: minmax(0, 1.55fr) repeat(3, minmax(0, 1fr));
  gap: 48px;
  padding-bottom: 48px;
}

.footer-brand .brand {
  margin-bottom: 18px;
  color: #fff;
}

.footer-brand .brand-text strong {
  color: #fff;
}

.footer-brand .brand-text small {
  color: #8fc4f7;
}

.footer-brand p {
  max-width: 380px;
  color: var(--dark-muted);
  font-size: 14px;
  line-height: 1.85;
}

.footer-brand .footer-contact {
  margin-top: 14px;
  font-size: 13px;
}

.footer-contact a {
  color: #c9d8eb;
  text-decoration: underline;
  text-underline-offset: 3px;
}

.footer-contact a:hover {
  color: #fff;
}

.footer-title {
  margin-bottom: 16px;
  color: #fff;
  font-size: 13px;
  font-weight: 600;
  letter-spacing: 0.08em;
}

.footer-col ul {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.footer-col a {
  color: var(--dark-muted);
  font-size: 14px;
  transition: color 0.25s ease-out;
}

.footer-col a:hover {
  color: #fff;
}

.footer-bottom {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
  padding: 22px 0 30px;
  border-top: 1px solid rgba(255, 255, 255, 0.12);
}

.footer-bottom p {
  color: #7f8da3;
  font-size: 12px;
  line-height: 1.7;
}

.footer-bottom p:last-child {
  text-align: right;
}

.back-to-top {
  position: fixed;
  right: 22px;
  bottom: 22px;
  z-index: 90;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 46px;
  height: 46px;
  border: 1px solid var(--border-light);
  border-radius: 50%;
  background: rgba(255, 255, 255, 0.95);
  color: var(--primary-strong);
  box-shadow: 0 8px 22px -12px rgba(27, 33, 52, 0.4);
  opacity: 0;
  visibility: hidden;
  transform: translateY(10px);
  transition: opacity 0.3s ease-out, transform 0.3s var(--ease), visibility 0.3s;
}

.back-to-top.is-visible {
  opacity: 1;
  visibility: visible;
  transform: none;
}

.back-to-top:hover {
  background: var(--primary-strong);
  color: #fff;
}

.back-to-top svg {
  width: 20px;
  height: 20px;
}

/* --------------------------------------------------------------------------
   页内零件
   -------------------------------------------------------------------------- */

.split {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(0, 1fr);
  gap: 48px;
  align-items: start;
}

.split--wide {
  grid-template-columns: minmax(0, 1.15fr) minmax(0, 0.85fr);
}

.split h2 {
  font-size: clamp(27px, 3.2vw, 38px);
  font-weight: 700;
  line-height: 1.25;
  letter-spacing: -0.02em;
}

.split p {
  color: var(--text-muted);
  font-size: 15.5px;
  line-height: 1.9;
}

.split p + p {
  margin-top: 12px;
}

.split .button {
  margin-top: 22px;
}

.mini-stats {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 14px;
  margin-top: 28px;
}

.mini-stat {
  padding: 18px;
  border: 1px solid var(--border-light);
  border-radius: var(--radius-md);
  background: var(--white);
}

.mini-stat strong {
  display: block;
  color: var(--primary-deep);
  font-family: var(--font-num);
  font-size: 26px;
  font-weight: 600;
  line-height: 1.15;
  font-variant-numeric: tabular-nums;
}

.mini-stat span {
  display: block;
  margin-top: 4px;
  color: var(--text-soft);
  font-size: 12px;
  line-height: 1.5;
}

.timeline {
  border-left: 1px solid var(--border);
  padding-left: 26px;
}

.timeline li {
  position: relative;
  padding-bottom: 22px;
}

.timeline li:last-child {
  padding-bottom: 0;
}

.timeline li::before {
  content: "";
  position: absolute;
  left: -31px;
  top: 8px;
  width: 9px;
  height: 9px;
  border: 2px solid var(--white);
  border-radius: 50%;
  background: var(--primary);
  box-shadow: 0 0 0 1px var(--primary);
}

.timeline time {
  display: block;
  color: var(--primary-deep);
  font-family: var(--font-num);
  font-size: 12px;
  font-weight: 600;
}

.timeline strong {
  display: block;
  margin-top: 2px;
  color: var(--text);
  font-size: 15px;
}

.timeline p {
  margin-top: 3px;
  color: var(--text-muted);
  font-size: 14px;
  line-height: 1.8;
}

/* 404 */
.not-found {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  min-height: 58vh;
  padding: 70px 0 90px;
  text-align: center;
}

.not-found .code {
  color: var(--primary-deep);
  font-family: var(--font-num);
  font-size: clamp(76px, 14vw, 132px);
  font-weight: 600;
  line-height: 1;
  letter-spacing: -0.06em;
  opacity: 0.25;
}

.not-found h1 {
  margin-top: 10px;
  font-size: clamp(30px, 4vw, 44px);
  letter-spacing: -0.02em;
}

.not-found p {
  max-width: 560px;
  margin-top: 14px;
  color: var(--text-muted);
  font-size: 16px;
}

.not-found .cta-actions {
  justify-content: center;
}

.not-found .button {
  margin-top: 0;
}

/* 首屏下方速览 */
.quick-facts {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 1px;
  overflow: hidden;
  border: 1px solid var(--border-light);
  border-radius: var(--radius-md);
  background: var(--border-light);
}

.quick-fact {
  padding: 24px;
  background: var(--white);
}

.quick-fact strong {
  display: block;
  color: var(--primary-deep);
  font-family: var(--font-num);
  font-size: 30px;
  font-weight: 600;
  line-height: 1.2;
}

.quick-fact span {
  display: block;
  margin-top: 3px;
  color: var(--text-soft);
  font-size: 12.5px;
}

.quick-fact p {
  margin-top: 12px;
  color: var(--text-muted);
  font-size: 14px;
  line-height: 1.75;
}

/* 滚动渐显 */
.reveal {
  opacity: 0;
  transform: translateY(16px);
  transition: opacity 0.6s var(--ease), transform 0.6s var(--ease);
  transition-delay: var(--reveal-delay, 0ms);
}

.reveal.is-visible {
  opacity: 1;
  transform: none;
}

/* --------------------------------------------------------------------------
   响应式
   -------------------------------------------------------------------------- */

@media (max-width: 1180px) {
  .site-nav ul {
    gap: 20px;
  }

  .nav-link {
    font-size: 14px;
  }
}

@media (min-width: 900px) {
  .split .table-wrap table {
    min-width: 0;
  }
}

@media (max-width: 1080px) {
  :root {
    --header-h: 68px;
  }

  .header-inner {
    width: calc(100% - 40px);
    min-height: var(--header-h);
  }

  .nav-toggle {
    display: block;
  }

  .site-nav {
    position: fixed;
    top: var(--header-h);
    left: 0;
    right: 0;
    z-index: 99;
    display: block;
    max-height: calc(100vh - var(--header-h));
    overflow-y: auto;
    padding: 8px 20px 22px;
    background: #fff;
    border-bottom: 1px solid var(--border-light);
    box-shadow: 0 20px 30px -25px rgba(27, 33, 52, 0.45);
    opacity: 0;
    visibility: hidden;
    transform: translateY(-8px);
    transition: opacity 0.25s ease-out, transform 0.25s var(--ease), visibility 0.25s;
  }

  .site-nav.is-open {
    opacity: 1;
    visibility: visible;
    transform: none;
  }

  .site-nav ul {
    display: block;
  }

  .site-nav li {
    border-bottom: 1px solid var(--border-light);
  }

  .site-nav li:last-child {
    border-bottom: 0;
  }

  .nav-link {
    display: block;
    padding: 15px 4px;
    font-size: 15px;
  }

  .nav-link::after {
    display: none;
  }

  .hero {
    padding: 48px 0 68px;
  }

  .hero h1 {
    font-size: clamp(40px, 6.4vw, 58px);
  }

  .grid--4 {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .steps {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .article-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .footer-grid {
    grid-template-columns: 1.4fr repeat(3, 1fr);
    gap: 32px;
  }
}

@media (max-width: 900px) {
  .container,
  .container--narrow,
  .hero-inner,
  .calc-shell--wide {
    width: calc(100% - 40px);
  }

  .section {
    padding: 64px 0;
  }

  .section--tight {
    padding: 52px 0;
  }

  .grid--3 {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .calc-results {
    grid-template-columns: 1fr;
  }

  .result-main {
    min-height: 160px;
  }

  .formula-box {
    grid-template-columns: 1fr;
  }

  .split,
  .split--wide {
    grid-template-columns: 1fr;
    gap: 28px;
  }

  .cta-inner {
    flex-direction: column;
    align-items: flex-start;
    gap: 26px;
  }

  .footer-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .footer-brand {
    grid-column: 1 / -1;
  }

  .footer-bottom {
    flex-direction: column;
    align-items: flex-start;
    gap: 8px;
  }

  .footer-bottom p:last-child {
    text-align: left;
  }

  .convert-grid {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 680px) {
  body {
    font-size: 16px;
  }

  .container,
  .container--narrow,
  .hero-inner,
  .calc-shell--wide {
    width: calc(100% - 32px);
  }

  .header-inner {
    width: calc(100% - 32px);
  }

  .brand-mark {
    width: 38px;
    height: 38px;
    flex-basis: 38px;
  }

  .brand-text strong {
    font-size: 17px;
  }

  .hero {
    padding: 38px 0 56px;
  }

  .hero h1 {
    font-size: clamp(36px, 10vw, 46px);
    letter-spacing: -0.03em;
  }

  .hero-lead {
    margin: 16px auto 28px;
    font-size: 16px;
    line-height: 1.8;
  }

  .hero-deco {
    right: -140px;
    width: 420px;
    opacity: 0.13;
  }

  .calc-card {
    padding: 20px;
  }

  .calc-head {
    flex-direction: column;
    gap: 10px;
  }

  .calc-sample {
  margin-top: 5px;
  color: var(--text-soft);
  font-size: 12px;
  line-height: 1.6;
}

.calc-badge {
    margin-top: 0;
  }

  .calc-grid,
  .calc-grid--two {
    grid-template-columns: 1fr;
    gap: 16px;
  }

  .input-wrap input {
    height: 52px;
  }

  .calc-actions {
    display: grid;
    grid-template-columns: 1fr 1fr;
  }

  .calc-actions .button {
    width: 100%;
  }

  .calc-actions .button--primary {
    grid-column: 1 / -1;
  }

  .result-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .result-item {
    min-height: 80px;
    padding: 12px 14px;
  }

  .result-item strong {
    font-size: 19px;
  }

  .result-number {
    font-size: 48px;
  }

  .calc-tabs {
    display: flex;
    width: 100%;
    overflow-x: auto;
  }

  .calc-tab {
    flex: 1 0 auto;
    padding: 0 12px;
    font-size: 13px;
  }

  .calc-intro-note {
    font-size: 12.5px;
  }

  .page-hero {
    padding: 24px 0 42px;
  }

  .page-hero h1 {
    font-size: clamp(30px, 8vw, 38px);
  }

  .page-lead {
    font-size: 16px;
    line-height: 1.8;
  }

  .breadcrumb {
    margin-bottom: 20px;
  }

  .section {
    padding: 52px 0;
  }

  .section-head {
    margin-bottom: 30px;
  }

  .section-head h2 {
    font-size: clamp(26px, 7vw, 32px);
  }

  .section-head .section-lead {
    font-size: 15.5px;
  }

  .grid--2,
  .grid--3,
  .grid--4 {
    grid-template-columns: 1fr;
  }

  .card {
    padding: 22px;
  }

  .steps {
    grid-template-columns: 1fr;
  }

  .checklist {
    grid-template-columns: 1fr;
  }

  .article-grid {
    grid-template-columns: 1fr;
  }

  .related-links {
    grid-template-columns: 1fr;
  }

  .quick-facts {
    grid-template-columns: 1fr;
  }

  .mini-stats {
    grid-template-columns: 1fr;
  }

  .convert-card {
    padding: 20px;
  }

  .convert-out,
  .convert-out--two {
    grid-template-columns: 1fr;
  }

  .cta-band {
    padding: 46px 0;
  }

  .cta-actions {
    width: 100%;
  }

  .cta-actions .button {
    width: 100%;
  }

  .footer-grid {
    grid-template-columns: 1fr;
    gap: 28px;
    padding-bottom: 36px;
  }

  .footer-brand {
    grid-column: auto;
  }

  .footer-bottom {
    padding-bottom: 24px;
  }

  .back-to-top {
    right: 14px;
    bottom: 14px;
    width: 42px;
    height: 42px;
  }

  .prose {
    font-size: 16px;
    line-height: 1.9;
  }

  .prose h2 {
    margin-top: 42px;
  }

  .faq-item summary {
    font-size: 15.5px;
    padding-right: 42px;
  }

  .faq-answer {
    padding-right: 0;
  }

  .table-wrap table {
    min-width: 520px;
  }

  .article-hero {
    padding: 24px 0 34px;
  }
}

@media (max-width: 400px) {
  .brand-text small {
    display: none;
  }
}

@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }

  *,
  *::before,
  *::after {
    animation-duration: 0.001ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.001ms !important;
  }

  .reveal {
    opacity: 1;
    transform: none;
  }
}

@media print {
  .site-header,
  .site-footer,
  .back-to-top,
  .calc-actions,
  .cta-band {
    display: none !important;
  }

  body {
    background: #fff;
    font-size: 12pt;
  }

  .section {
    padding: 20px 0;
  }

  .card,
  .table-wrap {
    break-inside: avoid;
  }
}