/* =========================================================
 * cpp-studio-zhangjh · 全站共享样式
 * 浅色 / 深色双主题：通过 <html data-theme="..."> 切换
 * 新增页面只需引用本文件，沿用同一套视觉变量
 * ========================================================= */

/* ---------- 设计变量 ---------- */
:root {
  --bg: #f6f8fb;
  --bg-soft: #eef2f7;
  --surface: #ffffff;
  --surface-2: #f8fafc;
  --text: #17233b;
  --text-2: #5c6b82;
  --text-3: #8a97ab;
  --border: #e2e8f0;
  --border-strong: #cbd5e1;

  --accent: #00599c;          /* C++ 官方蓝 */
  --accent-strong: #004d88;
  --accent-soft: rgba(0, 89, 156, 0.09);
  --accent-2: #0e9bb5;        /* 辅助青 */
  --accent-2-soft: rgba(14, 155, 181, 0.1);

  --code-bg: #0d1420;         /* 代码窗固定深色，编辑器质感 */
  --code-border: #1f2b3d;
  --code-text: #d6e2f0;
  --cl-kw: #7dd3fc;           /* 关键字 */
  --cl-typ: #a5b4fc;          /* 类型 */
  --cl-str: #86efac;          /* 字符串 */
  --cl-num: #fca5a5;          /* 数字 */
  --cl-cmt: #64748b;          /* 注释 */
  --cl-fn: #fbbf24;           /* 函数 */

  --shadow-sm: 0 1px 2px rgba(15, 23, 42, 0.06);
  --shadow-md: 0 6px 20px -6px rgba(15, 23, 42, 0.12);
  --shadow-lg: 0 16px 40px -12px rgba(15, 23, 42, 0.18);

  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 18px;

  --header-h: 64px;
  --font-sans: system-ui, -apple-system, "Segoe UI", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  --font-mono: ui-monospace, "Cascadia Code", "JetBrains Mono", "SF Mono", Consolas, "Courier New", monospace;
}

[data-theme="dark"] {
  --bg: #0b1017;
  --bg-soft: #0f1520;
  --surface: #131a26;
  --surface-2: #172032;
  --text: #e5edf7;
  --text-2: #9aabc2;
  --text-3: #6b7c93;
  --border: #223044;
  --border-strong: #2e3f57;

  --accent: #58a6e8;
  --accent-strong: #7bbdf5;
  --accent-soft: rgba(88, 166, 232, 0.14);
  --accent-2: #38bdd4;
  --accent-2-soft: rgba(56, 189, 212, 0.14);

  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.4);
  --shadow-md: 0 6px 20px -6px rgba(0, 0, 0, 0.5);
  --shadow-lg: 0 16px 40px -12px rgba(0, 0, 0, 0.6);
}

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

html {
  scroll-behavior: smooth;
  scroll-padding-top: calc(var(--header-h) + 16px);
}

body {
  margin: 0;
  font-family: var(--font-sans);
  background: var(--bg);
  color: var(--text);
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
  transition: background-color 0.3s ease, color 0.3s ease;
}

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

a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

h1, h2, h3 { line-height: 1.25; margin: 0; }
p { margin: 0; }
ul { margin: 0; padding: 0; list-style: none; }

.container {
  width: 100%;
  max-width: 1080px;
  margin-inline: auto;
  padding-inline: 24px;
}

.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: absolute;
  top: -48px;
  left: 16px;
  z-index: 200;
  padding: 8px 16px;
  background: var(--accent);
  color: #fff;
  border-radius: var(--radius-sm);
  transition: top 0.2s ease;
}
.skip-link:focus { top: 12px; }

:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
  border-radius: 4px;
}

/* ---------- 按钮 ---------- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 12px 26px;
  border-radius: 999px;
  font-size: 15px;
  font-weight: 600;
  font-family: inherit;
  cursor: pointer;
  border: 1.5px solid transparent;
  transition: transform 0.18s ease, box-shadow 0.18s ease, background-color 0.18s ease, border-color 0.18s ease, color 0.18s ease;
  text-decoration: none;
}
.btn:hover { text-decoration: none; transform: translateY(-2px); }
.btn:active { transform: translateY(0); }

.btn-primary {
  background: var(--accent);
  color: #fff;
  box-shadow: var(--shadow-md);
}
.btn-primary:hover { background: var(--accent-strong); box-shadow: var(--shadow-lg); }

.btn-ghost {
  background: transparent;
  color: var(--text);
  border-color: var(--border-strong);
}
.btn-ghost:hover { border-color: var(--accent); color: var(--accent); background: var(--accent-soft); }

/* ---------- 顶部导航 ---------- */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  height: var(--header-h);
  background: color-mix(in srgb, var(--bg) 82%, transparent);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid transparent;
  transition: border-color 0.25s ease, box-shadow 0.25s ease, background-color 0.25s ease;
}
.site-header.scrolled {
  border-bottom-color: var(--border);
  box-shadow: var(--shadow-sm);
  background: color-mix(in srgb, var(--bg) 92%, transparent);
}

.nav-inner {
  height: var(--header-h);
  display: flex;
  align-items: center;
  gap: 20px;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  color: var(--text);
  font-weight: 700;
  font-size: 16px;
  font-family: var(--font-mono);
  flex-shrink: 0;
}
.brand-logo-img {
  width: 26px;
  height: 26px;
  border-radius: 7px;
  flex-shrink: 0;
}

.brand:hover { text-decoration: none; color: var(--accent); }

.brand-logo {
  display: inline-grid;
  place-items: center;
  width: 32px; height: 32px;
  border-radius: 8px;
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  color: #fff;
  font-size: 12px;
  font-weight: 700;
}

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

.nav-menu {
  display: flex;
  align-items: center;
  gap: 4px;
}

.nav-link {
  display: block;
  padding: 8px 14px;
  border-radius: 999px;
  font-size: 14.5px;
  color: var(--text-2);
  transition: color 0.15s ease, background-color 0.15s ease;
}
.nav-link:hover { color: var(--text); background: var(--accent-soft); text-decoration: none; }
.nav-link.active { color: var(--accent); background: var(--accent-soft); font-weight: 600; }

.nav-toggle {
  display: none;
  flex-direction: column;
  justify-content: center;
  gap: 5px;
  width: 40px; height: 40px;
  padding: 9px 8px;
  background: transparent;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  cursor: pointer;
}
.nav-toggle-bar {
  display: block;
  height: 2px;
  width: 100%;
  background: var(--text);
  border-radius: 2px;
  transition: transform 0.25s ease, opacity 0.2s ease;
}
.nav-toggle[aria-expanded="true"] .nav-toggle-bar:nth-child(1) { transform: translateY(7px) rotate(45deg); }
.nav-toggle[aria-expanded="true"] .nav-toggle-bar:nth-child(2) { opacity: 0; }
.nav-toggle[aria-expanded="true"] .nav-toggle-bar:nth-child(3) { transform: translateY(-7px) rotate(-45deg); }

.theme-toggle {
  display: grid;
  place-items: center;
  width: 38px; height: 38px;
  flex-shrink: 0;
  border: 1px solid var(--border);
  border-radius: 50%;
  background: var(--surface);
  color: var(--text-2);
  cursor: pointer;
  transition: color 0.15s ease, border-color 0.15s ease, transform 0.15s ease;
}
.theme-toggle:hover { color: var(--accent); border-color: var(--accent); transform: rotate(15deg); }

.icon-moon { display: none; }
[data-theme="dark"] .icon-sun { display: none; }
[data-theme="dark"] .icon-moon { display: block; }

/* ---------- Hero ---------- */
.hero {
  position: relative;
  padding: 88px 0 96px;
  overflow: hidden;
}

/* 网格纹理背景 */
.hero::before {
  content: "";
  position: absolute;
  inset: 0;
  background-image:
    linear-gradient(color-mix(in srgb, var(--border) 55%, transparent) 1px, transparent 1px),
    linear-gradient(90deg, color-mix(in srgb, var(--border) 55%, transparent) 1px, transparent 1px);
  background-size: 44px 44px;
  mask-image: radial-gradient(ellipse 80% 65% at 50% 20%, #000 30%, transparent 75%);
  -webkit-mask-image: radial-gradient(ellipse 80% 65% at 50% 20%, #000 30%, transparent 75%);
  pointer-events: none;
}

/* 顶部柔光 */
.hero::after {
  content: "";
  position: absolute;
  top: -180px;
  left: 50%;
  transform: translateX(-50%);
  width: 720px; height: 420px;
  background: radial-gradient(ellipse, var(--accent-soft), transparent 70%);
  pointer-events: none;
}

.hero-grid {
  position: relative;
  z-index: 1;
  display: grid;
  grid-template-columns: 1.05fr 0.95fr;
  gap: 56px;
  align-items: center;
}

.hero-eyebrow {
  font-family: var(--font-mono);
  font-size: 13px;
  font-weight: 600;
  letter-spacing: 0.12em;
  color: var(--accent);
  margin-bottom: 14px;
}

.hero-title {
  font-size: clamp(34px, 5vw, 52px);
  font-family: var(--font-mono);
  font-weight: 800;
  letter-spacing: -0.02em;
  background: linear-gradient(100deg, var(--text) 30%, var(--accent) 75%, var(--accent-2));
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
  color: transparent;
  margin-bottom: 18px;
}

.hero-subtitle {
  font-size: clamp(18px, 2.4vw, 22px);
  font-weight: 600;
  min-height: 1.6em;
  margin-bottom: 16px;
  color: var(--text);
}

.caret {
  display: inline-block;
  width: 2px;
  height: 1.1em;
  margin-left: 2px;
  vertical-align: text-bottom;
  background: var(--accent);
  animation: blink 1s step-end infinite;
}
.caret.hidden { opacity: 0; }
@keyframes blink { 50% { opacity: 0; } }

.hero-desc {
  font-size: 16px;
  color: var(--text-2);
  max-width: 46em;
  margin-bottom: 32px;
}

.hero-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 14px;
}

/* ---------- 品牌签名区 ---------- */
.hero-brand { padding: 128px 0 140px; }

.signature-card {
  margin: 0;
  display: flex;
  justify-content: center;
}

/* 签名图为黑底浅字：衬一张深色"签名卡"，与黑底图标风格统一 */
.signature-card img {
  width: min(480px, 82vw);
  height: auto;
  background: #0a0e16;
  padding: 28px 36px;
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-lg);
  transition: transform 0.3s ease;
}
.signature-card img:hover { transform: translateY(-5px); }

/* ---------- 品牌头（手写签名 + 定位语） ---------- */
.brand-hero {
  display: flex;
  flex-direction: column;
  align-items: center;
  text-align: center;
}

.signature-hero img {
  width: min(520px, 84vw);
  padding: 32px 44px;
}

.brand-tagline {
  font-size: clamp(16px, 2vw, 19px);
  font-weight: 500;
  letter-spacing: 0.06em;
  color: var(--text-2);
  margin-top: 26px;
}

/* ---------- 代码窗口 ---------- */
.code-window {
  border-radius: var(--radius-lg);
  overflow: hidden;
  background: var(--code-bg);
  border: 1px solid var(--code-border);
  box-shadow: var(--shadow-lg);
  transform: rotate(0.4deg);
  transition: transform 0.3s ease;
}
.code-window:hover { transform: rotate(0deg) translateY(-4px); }

.code-titlebar {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 12px 16px;
  background: color-mix(in srgb, var(--code-bg) 80%, #ffffff 4%);
  border-bottom: 1px solid var(--code-border);
}
.dot { width: 11px; height: 11px; border-radius: 50%; }
.dot-red { background: #ff5f57; }
.dot-yellow { background: #febc2e; }
.dot-green { background: #28c840; }
.code-filename {
  margin-left: 8px;
  font-family: var(--font-mono);
  font-size: 12.5px;
  color: var(--code-text);
  opacity: 0.75;
}

.code-body {
  margin: 0;
  padding: 20px 22px 24px;
  font-family: var(--font-mono);
  font-size: 13.5px;
  line-height: 1.75;
  color: var(--code-text);
  overflow-x: auto;
}

/* 静态语法高亮 */
.cl-kw  { color: var(--cl-kw); }
.cl-typ { color: var(--cl-typ); }
.cl-str { color: var(--cl-str); }
.cl-num { color: var(--cl-num); }
.cl-cmt { color: var(--cl-cmt); font-style: italic; }
.cl-fn  { color: var(--cl-fn); }

/* ---------- 通用 Section ---------- */
.section { padding: 88px 0; }
.section-alt { background: var(--bg-soft); }

/* 子页面没有 hero，section 直接始于导航下方，补足顶部空间 */
.page-section { padding-top: 72px; }

.section-eyebrow {
  font-family: var(--font-mono);
  font-size: 13px;
  font-weight: 700;
  letter-spacing: 0.14em;
  color: var(--accent);
  margin-bottom: 10px;
}

.section-title {
  font-size: clamp(26px, 3.4vw, 34px);
  font-weight: 750;
  margin-bottom: 14px;
}

.section-desc {
  font-size: 16px;
  color: var(--text-2);
  max-width: 44em;
  margin-bottom: 44px;
}

/* ---------- 关于 ---------- */
.about-grid {
  display: grid;
  grid-template-columns: 1.15fr 0.85fr;
  gap: 48px;
  align-items: start;
}

.about-text p { font-size: 16px; color: var(--text-2); margin-bottom: 16px; }
.about-text strong { color: var(--text); }

.about-facts {
  display: grid;
  gap: 12px;
  padding: 24px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-sm);
}
.about-facts li {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  gap: 16px;
  padding-bottom: 12px;
  border-bottom: 1px dashed var(--border);
  font-size: 14.5px;
}
.about-facts li:last-child { padding-bottom: 0; border-bottom: none; }

.about-facts-wide { margin-top: 40px; }
.fact-label { color: var(--text-3); flex-shrink: 0; }
.fact-value { color: var(--text); font-weight: 600; text-align: right; }

/* ---------- 内容方向卡片 ---------- */
.card-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 20px;
}

.card {
  display: flex;
  flex-direction: column;
  gap: 12px;
  padding: 26px 24px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-sm);
  transition: transform 0.22s ease, box-shadow 0.22s ease, border-color 0.22s ease;
}
.card:hover {
  transform: translateY(-6px);
  box-shadow: var(--shadow-md);
  border-color: color-mix(in srgb, var(--accent) 45%, var(--border));
}

.card-icon {
  display: grid;
  place-items: center;
  width: 44px; height: 44px;
  border-radius: var(--radius-md);
  background: var(--accent-soft);
  color: var(--accent);
  font-family: var(--font-mono);
  font-weight: 700;
  font-size: 15px;
  margin-bottom: 4px;
}

.card-title { font-size: 18px; font-weight: 700; }
.card-text { font-size: 14.5px; color: var(--text-2); flex: 1; }

.card-tags { display: flex; flex-wrap: wrap; gap: 6px; margin-top: 4px; }
.card-tags li {
  padding: 3px 10px;
  font-size: 12px;
  border-radius: 999px;
  background: var(--surface-2);
  border: 1px solid var(--border);
  color: var(--text-2);
}

/* ---------- 精选内容列表 ---------- */
.post-list { display: grid; gap: 14px; }

.post-item {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  transition: transform 0.2s ease, box-shadow 0.2s ease, border-color 0.2s ease;
}
.post-item:hover {
  transform: translateX(6px);
  box-shadow: var(--shadow-md);
  border-color: color-mix(in srgb, var(--accent) 45%, var(--border));
}

.post-link {
  display: grid;
  grid-template-columns: auto 1fr;
  grid-template-rows: auto auto;
  column-gap: 18px;
  align-items: baseline;
  padding: 20px 24px;
  color: var(--text);
}
.post-link:hover { text-decoration: none; }

.post-cat {
  grid-row: span 2;
  align-self: center;
  padding: 5px 12px;
  font-size: 12.5px;
  font-weight: 600;
  border-radius: 999px;
  white-space: nowrap;
}
.post-cat-basic  { background: var(--accent-soft); color: var(--accent); }
.post-cat-modern { background: var(--accent-2-soft); color: var(--accent-2); }
.post-cat-eng    { background: rgba(124, 92, 246, 0.12); color: #7c5cf6; }
.post-cat-acm    { background: rgba(234, 138, 20, 0.13); color: #c77700; }
[data-theme="dark"] .post-cat-eng  { color: #a78bfa; }
[data-theme="dark"] .post-cat-acm  { color: #f0a63c; }

.post-title { font-size: 17px; font-weight: 650; }
.post-link:hover .post-title { color: var(--accent); }
.post-desc {
  grid-column: 2;
  font-size: 14px;
  color: var(--text-2);
  margin-top: 4px;
}

/* ---------- 个人作品卡片 ---------- */
.work-card {
  display: grid;
  grid-template-columns: 0.9fr 1.1fr;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  overflow: hidden;
  box-shadow: var(--shadow-sm);
  transition: transform 0.25s ease, box-shadow 0.25s ease;
}
.work-card:hover { transform: translateY(-5px); box-shadow: var(--shadow-md); }

.work-cover-link { display: block; overflow: hidden; }

.work-cover {
  width: 100%;
  height: 100%;
  min-height: 220px;
  object-fit: cover;
  transition: transform 0.4s ease;
}
.work-card:hover .work-cover { transform: scale(1.04); }

.work-body {
  display: flex;
  flex-direction: column;
  align-items: flex-start;
  gap: 14px;
  padding: 28px 30px;
}

.work-head {
  display: flex;
  align-items: center;
  gap: 12px;
}

.work-icon { width: 36px; height: 36px; border-radius: 8px; flex-shrink: 0; object-fit: contain; }

.work-title { font-size: 20px; font-weight: 750; }

.work-badge {
  padding: 3px 10px;
  font-size: 12px;
  font-weight: 600;
  border-radius: 999px;
  background: var(--accent-soft);
  color: var(--accent);
  white-space: nowrap;
}

.work-desc { font-size: 14.5px; color: var(--text-2); }

.work-tags { display: flex; flex-wrap: wrap; gap: 6px; }
.work-tags li {
  padding: 3px 10px;
  font-size: 12px;
  border-radius: 999px;
  background: var(--surface-2);
  border: 1px solid var(--border);
  color: var(--text-2);
}

.work-link {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  margin-top: auto;
  font-size: 14.5px;
  font-weight: 650;
  color: var(--accent);
}
.work-link:hover { text-decoration: underline; }

/* ---------- 作品入口卡（首页 → 作品页） ---------- */
.work-entry {
  display: flex;
  align-items: center;
  gap: 18px;
  padding: 22px 26px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-sm);
  color: var(--text);
  transition: transform 0.22s ease, box-shadow 0.22s ease, border-color 0.22s ease;
}
.work-entry:hover {
  text-decoration: none;
  transform: translateY(-4px);
  box-shadow: var(--shadow-md);
  border-color: color-mix(in srgb, var(--accent) 45%, var(--border));
}

.work-entry-icon { flex-shrink: 0; object-fit: contain; }

.work-entry-body {
  display: flex;
  flex-direction: column;
  gap: 4px;
  min-width: 0;
}
.work-entry-title { font-size: 18px; font-weight: 700; }
.work-entry-desc { font-size: 14px; color: var(--text-2); }

.work-entry-arrow {
  margin-left: auto;
  display: grid;
  place-items: center;
  width: 38px;
  height: 38px;
  border-radius: 50%;
  background: var(--accent-soft);
  color: var(--accent);
  flex-shrink: 0;
  transition: transform 0.2s ease;
}
.work-entry:hover .work-entry-arrow { transform: translate(3px, -3px); }

.works-more {
  margin-top: 28px;
  font-size: 14.5px;
  color: var(--text-3);
  text-align: center;
}

/* ---------- 数据统计 ---------- */
.stats-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 20px;
}

.stat {
  text-align: center;
  padding: 34px 16px 28px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-sm);
  transition: transform 0.22s ease, box-shadow 0.22s ease;
}
.stat:hover { transform: translateY(-5px); box-shadow: var(--shadow-md); }

.stat-num {
  font-family: var(--font-mono);
  font-size: clamp(34px, 4vw, 44px);
  font-weight: 800;
  color: var(--accent);
  letter-spacing: -0.02em;
}
.stat-unit {
  font-size: 15px;
  font-weight: 600;
  color: var(--text-2);
  margin-left: 4px;
}
.stat-label { font-size: 14px; color: var(--text-2); margin-top: 6px; }

/* ---------- 联系 ---------- */
.contact-box {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 24px;
  text-align: center;
  padding: 56px 32px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-sm);
  background-image: radial-gradient(circle at 50% -60%, var(--accent-soft), transparent 60%);
}
.contact-text { font-size: 16.5px; color: var(--text-2); max-width: 40em; }

/* ---------- 页脚 ---------- */
.site-footer {
  border-top: 1px solid var(--border);
  background: var(--bg-soft);
  padding-top: 52px;
}

.footer-grid {
  display: grid;
  grid-template-columns: 1.4fr 1fr 1.2fr;
  gap: 40px;
  padding-bottom: 40px;
}

.footer-brand { display: grid; gap: 10px; align-content: start; }
.footer-brand .brand-logo { width: 34px; height: 34px; font-size: 13px; }
.footer-brand-name { font-family: var(--font-mono); font-weight: 700; font-size: 15px; }
.footer-brand-desc { font-size: 14px; color: var(--text-2); }

.footer-heading {
  font-size: 13px;
  font-weight: 700;
  letter-spacing: 0.08em;
  color: var(--text-3);
  text-transform: uppercase;
  margin-bottom: 14px;
}

.footer-nav ul { display: grid; gap: 9px; }
.footer-nav a { font-size: 14.5px; color: var(--text-2); }
.footer-nav a:hover { color: var(--accent); }

.footer-note p:last-child { font-size: 14px; color: var(--text-2); }

.footer-bottom {
  padding: 20px 24px;
  border-top: 1px solid var(--border);
  font-size: 13px;
  color: var(--text-3);
  text-align: center;
}

/* ---------- 返回顶部 ---------- */
.back-to-top {
  position: fixed;
  right: 24px;
  bottom: 24px;
  z-index: 90;
  display: grid;
  place-items: center;
  width: 42px; height: 42px;
  border-radius: 50%;
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text-2);
  cursor: pointer;
  box-shadow: var(--shadow-md);
  opacity: 0;
  visibility: hidden;
  transform: translateY(12px);
  transition: opacity 0.25s ease, transform 0.25s ease, visibility 0.25s ease, color 0.15s ease, border-color 0.15s ease;
}
.back-to-top.show { opacity: 1; visibility: visible; transform: translateY(0); }
.back-to-top:hover { color: var(--accent); border-color: var(--accent); }

/* ---------- 滚动显现动画 ---------- */
.reveal {
  opacity: 0;
  transform: translateY(22px);
  transition: opacity 0.6s ease, transform 0.6s ease;
}
.reveal.visible { opacity: 1; transform: none; }

/* ---------- 响应式 ---------- */
@media (max-width: 960px) {
  .card-grid, .stats-grid { grid-template-columns: repeat(2, 1fr); }
  .hero-grid { grid-template-columns: 1fr; gap: 44px; }
  .hero-code { max-width: 560px; }
  .about-grid { grid-template-columns: 1fr; gap: 28px; }
  .work-card { grid-template-columns: 1fr; }
}

@media (max-width: 720px) {
  .nav-toggle { display: flex; }
  .nav-inner { gap: 12px; }
  .site-header nav { margin-left: auto; }

  .nav-menu {
    position: absolute;
    top: var(--header-h);
    left: 0;
    right: 0;
    flex-direction: column;
    align-items: stretch;
    gap: 2px;
    padding: 10px 24px 16px;
    background: var(--surface);
    border-bottom: 1px solid var(--border);
    box-shadow: var(--shadow-md);
    display: none;
  }
  .nav-menu.open { display: flex; }
  .nav-link { padding: 11px 14px; border-radius: var(--radius-sm); }

  .hero { padding: 56px 0 64px; }
  .section { padding: 60px 0; }
  .section-desc { margin-bottom: 32px; }

  .post-link { grid-template-columns: 1fr; row-gap: 8px; padding: 18px 20px; }
  .post-cat { grid-row: auto; justify-self: start; }
  .post-desc { grid-column: 1; }

  .footer-grid { grid-template-columns: 1fr; gap: 28px; }
  .contact-box { padding: 40px 22px; }
}

@media (max-width: 480px) {
  .card-grid, .stats-grid { grid-template-columns: 1fr; }
  .brand-name { display: none; }
  .hero-actions .btn { width: 100%; }
}

/* ---------- 动效减弱偏好 ---------- */
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
  .reveal { opacity: 1; transform: none; }
}