/* ==========================================================================
   星轨科技官网 · 样式表
   结构：
   1. 设计令牌（CSS 变量）
   2. 基础重置
   3. 通用组件（容器/按钮/标题）
   4. 头部导航（含移动端抽屉）
   5. Hero
   6. Logo 墙
   7. 业务板块卡片
   8. 优势 + 数据
   9. 案例
   10. 关于我们
   11. 联系表单
   12. 页脚 / 回到顶部
   13. 动效与响应式断点
   ========================================================================== */

/* ---------- 1. 设计令牌 ---------- */
:root {
  /* 颜色（深色背景 + 蓝色主色，适合 B 端科技企业） */
  --c-bg: #0a1020;
  --c-bg-alt: #0d1526;
  --c-surface: #111c31;
  --c-surface-2: #16233c;
  --c-border: #22304d;
  --c-text: #e8eefc;
  --c-text-dim: #9aabc6;
  --c-text-mute: #6f81a0;
  --c-primary: #5b8cff;
  --c-primary-dark: #3f6ee0;
  --c-accent: #22d3ee;
  --c-danger: #ff7a7a;
  --c-success: #4ade80;

  /* 排版 */
  --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC",
    "Hiragino Sans GB", "Microsoft YaHei", "Source Han Sans SC", sans-serif;
  --fs-base: 1rem;
  --lh-base: 1.75;

  /* 间距（8px 基准） */
  --sp-1: 0.5rem;
  --sp-2: 1rem;
  --sp-3: 1.5rem;
  --sp-4: 2rem;
  --sp-5: 3rem;
  --sp-6: 4rem;
  --sp-7: 6rem;

  /* 圆角 / 阴影 */
  --r-sm: 8px;
  --r-md: 12px;
  --r-lg: 18px;
  --r-full: 999px;
  --shadow-card: 0 1px 2px rgba(0, 0, 0, .3), 0 12px 32px -12px rgba(0, 0, 0, .55);
  --shadow-hover: 0 2px 4px rgba(0, 0, 0, .35), 0 24px 48px -16px rgba(91, 140, 255, .35);

  /* 布局 */
  --container: 1160px;
  --header-h: 72px;
}

/* ---------- 2. 基础重置 ---------- */
*,
*::before,
*::after { box-sizing: border-box; }

html {
  -webkit-text-size-adjust: 100%;
  scroll-behavior: smooth;
  /* 锚点跳转时避开固定头部 */
  scroll-padding-top: calc(var(--header-h) + 16px);
}

body {
  margin: 0;
  background: var(--c-bg);
  color: var(--c-text);
  font-family: var(--font-sans);
  font-size: var(--fs-base);
  line-height: var(--lh-base);
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
  overflow-x: hidden;
}

h1, h2, h3, h4 {
  margin: 0;
  line-height: 1.28;
  letter-spacing: -0.01em;
  font-weight: 700;
}

p { margin: 0; }
ul { margin: 0; padding: 0; list-style: none; }
a { color: inherit; text-decoration: none; }
img, svg { display: block; max-width: 100%; }
button { font: inherit; color: inherit; }

/* 键盘焦点可见 —— 无障碍必做，不要用 outline:none 抹掉 */
:focus-visible {
  outline: 2px solid var(--c-accent);
  outline-offset: 3px;
  border-radius: 4px;
}

::selection { background: rgba(91, 140, 255, .35); }

/* 跳转链接：仅键盘聚焦时出现 */
.skip-link {
  position: absolute;
  left: -9999px;
  top: 0;
  z-index: 200;
  padding: 12px 20px;
  background: var(--c-primary);
  color: #fff;
  border-radius: 0 0 var(--r-sm) 0;
}
.skip-link:focus { left: 0; }

/* ---------- 3. 通用组件 ---------- */
.container {
  width: 100%;
  max-width: var(--container);
  margin-inline: auto;
  padding-inline: 20px;
}

.section { padding-block: var(--sp-7); }
.section-alt { background: var(--c-bg-alt); border-block: 1px solid var(--c-border); }

.section-head {
  max-width: 720px;
  margin-bottom: var(--sp-5);
}

.section-eyebrow {
  display: inline-block;
  margin-bottom: var(--sp-1);
  font-size: 0.8125rem;
  font-weight: 600;
  letter-spacing: .12em;
  text-transform: uppercase;
  color: var(--c-accent);
}

.section-head h2,
.split-copy h2,
.contact-copy h2 {
  font-size: clamp(1.65rem, 3.4vw, 2.5rem);
  margin-bottom: var(--sp-2);
}

.section-desc {
  color: var(--c-text-dim);
  font-size: 1.0625rem;
}

/* 按钮 */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 12px 22px;
  border: 1px solid transparent;
  border-radius: var(--r-full);
  font-size: 0.9375rem;
  font-weight: 600;
  line-height: 1.2;
  white-space: nowrap;
  cursor: pointer;
  transition: transform .18s ease, background-color .18s ease,
              border-color .18s ease, box-shadow .18s ease;
}
.btn:active { transform: translateY(1px); }

.btn-primary {
  background: var(--c-primary);
  color: #fff;
  box-shadow: 0 8px 20px -8px rgba(91, 140, 255, .7);
}
.btn-primary:hover {
  background: var(--c-primary-dark);
  box-shadow: 0 12px 28px -8px rgba(91, 140, 255, .8);
}

.btn-outline {
  border-color: var(--c-border);
  color: var(--c-text);
  background: transparent;
}
.btn-outline:hover { border-color: var(--c-primary); background: rgba(91, 140, 255, .08); }

.btn-ghost { color: var(--c-text-dim); }
.btn-ghost:hover { color: var(--c-text); }

.btn-sm { padding: 9px 16px; font-size: 0.875rem; }
.btn-lg { padding: 15px 30px; font-size: 1rem; }
.btn-block { width: 100%; }

/* ---------- 4. 头部导航 ---------- */
.site-header {
  position: fixed;
  inset: 0 0 auto 0;
  z-index: 100;
  height: var(--header-h);
  display: flex;
  align-items: center;
  background: rgba(10, 16, 32, .55);
  backdrop-filter: blur(14px);
  -webkit-backdrop-filter: blur(14px);
  border-bottom: 1px solid transparent;
  transition: background-color .25s ease, border-color .25s ease;
}
/* 滚动后加深背景，保证内容可读 */
.site-header.is-scrolled {
  background: rgba(10, 16, 32, .92);
  border-bottom-color: var(--c-border);
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--sp-3);
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  font-weight: 700;
  font-size: 1.0625rem;
  letter-spacing: .01em;
}
.brand-mark { width: 30px; height: 30px; flex: none; }

.nav {
  display: flex;
  align-items: center;
  gap: var(--sp-4);
}

.nav-list {
  display: flex;
  align-items: center;
  gap: var(--sp-3);
}

.nav-link {
  position: relative;
  font-size: 0.9375rem;
  color: var(--c-text-dim);
  padding: 6px 2px;
  transition: color .18s ease;
}
.nav-link::after {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  bottom: 0;
  height: 2px;
  border-radius: 2px;
  background: var(--c-primary);
  transform: scaleX(0);
  transition: transform .22s ease;
}
.nav-link:hover,
.nav-link.is-active { color: var(--c-text); }
.nav-link:hover::after,
.nav-link.is-active::after { transform: scaleX(1); }

.nav-actions { display: flex; align-items: center; gap: var(--sp-1); }

/* 汉堡按钮：移动端显示 */
.menu-toggle {
  display: none;
  width: 44px;
  height: 44px;
  padding: 0;
  background: transparent;
  border: 1px solid var(--c-border);
  border-radius: var(--r-sm);
  cursor: pointer;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 5px;
}
.menu-bar {
  display: block;
  width: 18px;
  height: 2px;
  border-radius: 2px;
  background: var(--c-text);
  transition: transform .25s ease, opacity .2s ease;
}
.menu-toggle[aria-expanded="true"] .menu-bar:nth-child(1) { transform: translateY(7px) rotate(45deg); }
.menu-toggle[aria-expanded="true"] .menu-bar:nth-child(2) { opacity: 0; }
.menu-toggle[aria-expanded="true"] .menu-bar:nth-child(3) { transform: translateY(-7px) rotate(-45deg); }

/* ---------- 5. Hero ---------- */
.hero {
  position: relative;
  padding-top: calc(var(--header-h) + var(--sp-6));
  padding-bottom: var(--sp-7);
  overflow: hidden;
}

.hero-glow {
  position: absolute;
  top: -180px;
  right: -120px;
  width: 720px;
  height: 720px;
  border-radius: 50%;
  background: radial-gradient(circle, rgba(91, 140, 255, .28), transparent 62%);
  filter: blur(20px);
  pointer-events: none;
}

.hero-inner {
  position: relative;
  display: grid;
  grid-template-columns: 1.05fr 1fr;
  align-items: center;
  gap: var(--sp-6);
}

.eyebrow {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 6px 14px 6px 10px;
  margin-bottom: var(--sp-3);
  border: 1px solid var(--c-border);
  border-radius: var(--r-full);
  background: rgba(91, 140, 255, .08);
  font-size: 0.8125rem;
  color: var(--c-text-dim);
}
.eyebrow .dot {
  width: 7px;
  height: 7px;
  border-radius: 50%;
  background: var(--c-accent);
  box-shadow: 0 0 0 3px rgba(34, 211, 238, .2);
}

.hero h1 {
  font-size: clamp(2rem, 5.2vw, 3.35rem);
  letter-spacing: -0.025em;
  margin-bottom: var(--sp-3);
  background: linear-gradient(180deg, #ffffff 30%, #b9c9e6 100%);
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
}

.lede {
  max-width: 540px;
  color: var(--c-text-dim);
  font-size: 1.0625rem;
  margin-bottom: var(--sp-4);
}

.hero-cta {
  display: flex;
  flex-wrap: wrap;
  gap: var(--sp-2);
  margin-bottom: var(--sp-5);
}

.hero-trust {
  display: flex;
  flex-wrap: wrap;
  gap: var(--sp-4);
  padding-top: var(--sp-4);
  border-top: 1px solid var(--c-border);
}
.hero-trust li { display: flex; flex-direction: column; }
.hero-trust strong {
  font-size: 1.375rem;
  font-weight: 700;
  color: var(--c-text);
}
.hero-trust span { font-size: 0.8125rem; color: var(--c-text-mute); }

.hero-visual { position: relative; }
.dashboard {
  width: 100%;
  height: auto;
  filter: drop-shadow(0 30px 60px rgba(0, 0, 0, .5));
}

/* ---------- 6. Logo 墙 ---------- */
.logo-strip {
  padding-block: var(--sp-4);
  border-block: 1px solid var(--c-border);
  background: var(--c-bg-alt);
}
.logo-strip-title {
  text-align: center;
  font-size: 0.8125rem;
  letter-spacing: .08em;
  color: var(--c-text-mute);
  margin-bottom: var(--sp-3);
}
.logo-list {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: var(--sp-3) var(--sp-5);
}
.logo-list li {
  font-size: 1.0625rem;
  font-weight: 600;
  color: #5d6f8e;
  letter-spacing: .06em;
  transition: color .2s ease;
}
.logo-list li:hover { color: var(--c-text-dim); }

/* ---------- 7. 业务板块卡片 ---------- */
.cards-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--sp-3);
}

.card {
  position: relative;
  padding: var(--sp-4);
  background: var(--c-surface);
  border: 1px solid var(--c-border);
  border-radius: var(--r-lg);
  box-shadow: var(--shadow-card);
  transition: transform .25s ease, border-color .25s ease, box-shadow .25s ease;
}
.card:hover {
  transform: translateY(-4px);
  border-color: rgba(91, 140, 255, .5);
  box-shadow: var(--shadow-hover);
}

.card-icon {
  width: 44px;
  height: 44px;
  display: grid;
  place-items: center;
  margin-bottom: var(--sp-3);
  border-radius: var(--r-md);
  background: rgba(91, 140, 255, .12);
  color: var(--c-accent);
}
.card-icon svg { width: 24px; height: 24px; }

.card h3 { font-size: 1.1875rem; margin-bottom: var(--sp-1); }
.card > p { color: var(--c-text-dim); font-size: 0.9375rem; }

.card-list {
  margin-top: var(--sp-3);
  padding-top: var(--sp-3);
  border-top: 1px dashed var(--c-border);
  display: grid;
  gap: 8px;
}
.card-list li {
  position: relative;
  padding-left: 20px;
  font-size: 0.875rem;
  color: var(--c-text-mute);
}
.card-list li::before {
  content: "";
  position: absolute;
  left: 0;
  top: 9px;
  width: 7px;
  height: 7px;
  border-radius: 2px;
  background: var(--c-primary);
  opacity: .8;
}

/* ---------- 8. 优势 + 数据 ---------- */
.split {
  display: grid;
  grid-template-columns: 1fr 1fr;
  align-items: center;
  gap: var(--sp-6);
}

.check-list {
  display: grid;
  gap: 12px;
  margin-block: var(--sp-4);
}
.check-list li {
  position: relative;
  padding-left: 30px;
  color: var(--c-text-dim);
  font-size: 0.9375rem;
}
.check-list li::before {
  content: "";
  position: absolute;
  left: 0;
  top: 5px;
  width: 18px;
  height: 18px;
  border-radius: 50%;
  background: rgba(74, 222, 128, .14);
}
.check-list li::after {
  content: "";
  position: absolute;
  left: 5px;
  top: 10px;
  width: 8px;
  height: 4px;
  border-left: 2px solid var(--c-success);
  border-bottom: 2px solid var(--c-success);
  transform: rotate(-45deg);
}

.stats-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: var(--sp-2);
}
.stat {
  padding: var(--sp-3);
  background: var(--c-surface);
  border: 1px solid var(--c-border);
  border-radius: var(--r-md);
  display: flex;
  flex-direction: column;
  gap: 4px;
}
.stat-num {
  font-size: clamp(1.6rem, 3.6vw, 2.25rem);
  font-weight: 700;
  letter-spacing: -0.02em;
  color: var(--c-accent);
  font-variant-numeric: tabular-nums;
}
.stat-label { font-size: 0.875rem; color: var(--c-text-mute); }

/* ---------- 9. 案例 ---------- */
.cases {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--sp-3);
}
.case {
  display: flex;
  flex-direction: column;
  overflow: hidden;
  background: var(--c-surface);
  border: 1px solid var(--c-border);
  border-radius: var(--r-lg);
  transition: transform .25s ease, border-color .25s ease;
}
.case:hover { transform: translateY(-4px); border-color: rgba(91, 140, 255, .5); }

.case-thumb {
  aspect-ratio: 16 / 9;
  display: grid;
  place-items: center;
  background: linear-gradient(135deg, #1b3a6b, #122544);
  position: relative;
  overflow: hidden;
}
.case-thumb::before {
  content: "";
  position: absolute;
  inset: 0;
  background-image:
    linear-gradient(rgba(91, 140, 255, .16) 1px, transparent 1px),
    linear-gradient(90deg, rgba(91, 140, 255, .16) 1px, transparent 1px);
  background-size: 26px 26px;
}
.case-thumb.alt { background: linear-gradient(135deg, #1a3b52, #102434); }
.case-thumb.deep { background: linear-gradient(135deg, #22365c, #131d31); }
.case-thumb span {
  position: relative;
  padding: 6px 16px;
  border-radius: var(--r-full);
  background: rgba(10, 16, 32, .6);
  border: 1px solid rgba(255, 255, 255, .14);
  font-size: 0.8125rem;
  color: var(--c-text);
}

.case-body {
  display: flex;
  flex-direction: column;
  gap: var(--sp-1);
  padding: var(--sp-3);
  flex: 1;
}
.case-body h3 { font-size: 1.0625rem; }
.case-body p { font-size: 0.9375rem; color: var(--c-text-dim); }

.link-arrow {
  margin-top: auto;
  padding-top: var(--sp-2);
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--c-primary);
  display: inline-flex;
  align-items: center;
  gap: 6px;
}
.link-arrow span { transition: transform .2s ease; }
.link-arrow:hover span { transform: translateX(4px); }

/* ---------- 10. 关于我们 ---------- */
.split-reverse { grid-template-columns: .85fr 1.15fr; }

.team-visual {
  padding: var(--sp-4);
  border-radius: var(--r-lg);
  border: 1px solid var(--c-border);
  background:
    radial-gradient(circle at 20% 20%, rgba(91, 140, 255, .18), transparent 60%),
    var(--c-surface);
}
.avatar-row { display: flex; gap: -8px; }
.avatar {
  width: 64px;
  height: 64px;
  margin-right: -10px;
  border-radius: 50%;
  display: grid;
  place-items: center;
  font-weight: 700;
  color: #fff;
  border: 2px solid var(--c-surface);
  background: linear-gradient(135deg, #3f6ee0, #22d3ee);
}
.avatar:nth-child(2) { background: linear-gradient(135deg, #5b8cff, #7c5bff); }
.avatar:nth-child(3) { background: linear-gradient(135deg, #22d3ee, #4ade80); }
.avatar:nth-child(4) { background: linear-gradient(135deg, #7c5bff, #ef6ea8); }
.team-caption { margin-top: var(--sp-3); font-size: 0.875rem; color: var(--c-text-mute); }

.info-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: var(--sp-2);
  margin-top: var(--sp-4);
}
.info-grid > div {
  padding: var(--sp-2) var(--sp-3);
  border-left: 2px solid var(--c-primary);
  background: rgba(91, 140, 255, .05);
}
.info-k { display: block; font-size: 0.75rem; color: var(--c-text-mute); }
.info-v { font-weight: 600; font-size: 0.9375rem; }

/* ---------- 11. 联系表单 ---------- */
.contact-wrap {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--sp-6);
  align-items: start;
}

.contact-list {
  display: grid;
  gap: var(--sp-3);
  margin-top: var(--sp-4);
}
.contact-list li { display: flex; flex-direction: column; gap: 2px; }
.contact-k { font-size: 0.75rem; color: var(--c-text-mute); letter-spacing: .06em; }
.contact-list a { color: var(--c-text); font-weight: 600; }
.contact-list a:hover { color: var(--c-primary); }
.contact-list span:not(.contact-k) { color: var(--c-text-dim); }

.contact-form {
  padding: var(--sp-4);
  background: var(--c-surface);
  border: 1px solid var(--c-border);
  border-radius: var(--r-lg);
  box-shadow: var(--shadow-card);
  display: grid;
  gap: var(--sp-3);
}

.field { display: grid; gap: 6px; }
.field label {
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--c-text-dim);
}
.req { color: var(--c-danger); }

.field input,
.field textarea {
  width: 100%;
  padding: 12px 14px;
  background: var(--c-bg);
  border: 1px solid var(--c-border);
  border-radius: var(--r-sm);
  color: var(--c-text);
  font-family: inherit;
  font-size: 0.9375rem;
  transition: border-color .18s ease, box-shadow .18s ease;
}
.field textarea { resize: vertical; min-height: 110px; }
.field input::placeholder,
.field textarea::placeholder { color: #55637d; }

.field input:focus,
.field textarea:focus {
  outline: none;
  border-color: var(--c-primary);
  box-shadow: 0 0 0 3px rgba(91, 140, 255, .18);
}
/* 校验失败态 */
.field.has-error input,
.field.has-error textarea { border-color: var(--c-danger); }

.err {
  min-height: 0;
  font-size: 0.8125rem;
  color: var(--c-danger);
}
.err:empty { display: none; }

.form-note { font-size: 0.75rem; color: var(--c-text-mute); }
.form-status {
  font-size: 0.875rem;
  color: var(--c-success);
  min-height: 1.2em;
}

/* ---------- 12. 页脚 / 回到顶部 ---------- */
.site-footer {
  padding-top: var(--sp-6);
  background: #070c17;
  border-top: 1px solid var(--c-border);
}
.footer-inner {
  display: grid;
  grid-template-columns: 1.2fr 2fr;
  gap: var(--sp-5);
  padding-bottom: var(--sp-5);
}
.footer-brand p {
  margin-top: var(--sp-2);
  color: var(--c-text-mute);
  font-size: 0.875rem;
  max-width: 280px;
}
.footer-nav {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--sp-3);
}
.footer-nav h4 {
  font-size: 0.875rem;
  margin-bottom: var(--sp-2);
  color: var(--c-text);
}
.footer-nav ul { display: grid; gap: 10px; }
.footer-nav a { font-size: 0.875rem; color: var(--c-text-mute); }
.footer-nav a:hover { color: var(--c-primary); }

.footer-bottom {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: var(--sp-2);
  padding-block: var(--sp-3);
  border-top: 1px solid var(--c-border);
  font-size: 0.8125rem;
  color: var(--c-text-mute);
}
.footer-bottom a:hover { color: var(--c-text-dim); }
.sep { margin-inline: 8px; }

.back-top {
  position: fixed;
  right: 20px;
  bottom: 24px;
  z-index: 90;
  width: 46px;
  height: 46px;
  display: grid;
  place-items: center;
  border-radius: 50%;
  border: 1px solid var(--c-border);
  background: rgba(22, 35, 60, .9);
  backdrop-filter: blur(8px);
  color: var(--c-text);
  cursor: pointer;
  transition: opacity .25s ease, transform .25s ease, background-color .2s ease;
}
.back-top svg { width: 20px; height: 20px; }
.back-top:hover { background: var(--c-primary); border-color: var(--c-primary); }
.back-top[hidden] { display: none; }

/* ---------- 13. 动效与响应式 ---------- */

/* 滚动入场：元素初始略下移透明，进入视口后归位 */
.reveal {
  opacity: 0;
  transform: translateY(18px);
  transition: opacity .6s ease, transform .6s cubic-bezier(.22, .61, .36, 1);
  will-change: opacity, transform;
}
.reveal.is-visible {
  opacity: 1;
  transform: none;
}

/* 尊重系统「减少动态效果」设置 */
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *,
  *::before,
  *::after {
    animation-duration: .001ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: .001ms !important;
  }
  .reveal { opacity: 1; transform: none; }
}

/* 打印：去掉装饰，保留文字 */
@media print {
  .site-header, .back-top, .hero-glow, .hero-visual, .contact-form { display: none; }
  body { background: #fff; color: #000; }
}

/* ---- 平板 ---- */
@media (max-width: 992px) {
  :root { --sp-7: 4.5rem; }

  .hero-inner { grid-template-columns: 1fr; gap: var(--sp-5); }
  .hero-copy { max-width: 640px; }
  .hero-visual { max-width: 560px; }

  .cards-grid { grid-template-columns: repeat(2, 1fr); }
  .cases { grid-template-columns: repeat(2, 1fr); }
  .case:last-child { grid-column: 1 / -1; }
  .case:last-child .case-thumb { aspect-ratio: 21 / 9; }

  .split,
  .split-reverse { grid-template-columns: 1fr; gap: var(--sp-4); }
  .contact-wrap { grid-template-columns: 1fr; gap: var(--sp-4); }

  .footer-inner { grid-template-columns: 1fr; gap: var(--sp-4); }
}

/* ---- 手机 ---- */
@media (max-width: 768px) {
  :root {
    --sp-6: 3rem;
    --sp-7: 3.5rem;
    --header-h: 64px;
  }

  /* 导航改为下拉抽屉 */
  .menu-toggle { display: inline-flex; }

  .nav {
    position: fixed;
    inset: var(--header-h) 0 auto 0;
    flex-direction: column;
    align-items: stretch;
    gap: 0;
    padding: var(--sp-2) 20px var(--sp-3);
    background: rgba(9, 14, 27, .98);
    backdrop-filter: blur(16px);
    border-bottom: 1px solid var(--c-border);
    /* 用 transform 做位移动画，比改 height 更省性能 */
    transform: translateY(-8px);
    opacity: 0;
    visibility: hidden;
    pointer-events: none;
    transition: opacity .22s ease, transform .22s ease, visibility .22s;
    max-height: calc(100dvh - var(--header-h));
    overflow-y: auto;
  }
  .nav.is-open {
    transform: none;
    opacity: 1;
    visibility: visible;
    pointer-events: auto;
  }

  .nav-list {
    flex-direction: column;
    align-items: stretch;
    gap: 0;
  }
  .nav-link {
    display: block;
    padding: 14px 4px;
    font-size: 1rem;
    border-bottom: 1px solid rgba(34, 48, 77, .6);
  }
  .nav-link::after { display: none; }

  .nav-actions {
    margin-top: var(--sp-3);
    gap: 10px;
  }
  .nav-actions .btn { flex: 1; }

  .hero { padding-top: calc(var(--header-h) + var(--sp-4)); }
  .hero-cta .btn { flex: 1 1 100%; }
  .hero-trust { gap: var(--sp-3) var(--sp-4); }

  .cards-grid,
  .cases { grid-template-columns: 1fr; }
  .case:last-child .case-thumb { aspect-ratio: 16 / 9; }

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

  .footer-nav { grid-template-columns: repeat(2, 1fr); gap: var(--sp-3); }
  .footer-bottom { justify-content: flex-start; }

  .back-top { right: 14px; bottom: 16px; }
}

/* ---- 小屏微调 ---- */
@media (max-width: 380px) {
  .container { padding-inline: 16px; }
  .hero-trust { display: grid; grid-template-columns: 1fr 1fr; }
  .stats-grid { grid-template-columns: 1fr; }
}

/* ---- 大屏 ---- */
@media (min-width: 1440px) {
  :root { --container: 1240px; }
}