/* ============================================================
   一帖科技 yitie.net — 设计系统
   美学方向：东方编辑部（Oriental Editorial）
   ============================================================ */

/* --- 字体引入 --- */
/* 字体引入：已移至 HTML <link> 以优化首屏加载速度 */

/* ============================================================
   设计令牌 (Design Tokens)
   ============================================================ */
:root {
  /* --- 品牌色 --- */
  --color-camellia: #EE3F4D;
  /* 茶花红：仅作点睛 */
  --color-camellia-dim: #D4545F;
  /* 暗色模式下降饱和 */
  --color-horn: #2D2E36;
  /* 牛角灰 */
  --color-rice: #FAF5EB;
  /* 米白 */
  --color-ink: #1A1A20;
  /* 深墨（暗色背景） */
  --color-bone: #E8E6E1;
  /* 骨白（暗色文字） */

  /* --- KakaMind 子品牌色 --- */
  --color-coffee: #945833;
  --color-silver: #F1F0ED;

  /* --- 语义化色彩（亮色模式默认） --- */
  --bg-primary: var(--color-rice);
  --bg-secondary: #F3EDE0;
  --bg-nav: rgba(250, 245, 235, 0.85);
  --text-primary: var(--color-horn);
  --text-secondary: #5A5B66;
  --text-muted: #9A9AA0;
  --accent: var(--color-camellia);
  --border-subtle: rgba(45, 46, 54, 0.08);
  --shadow-soft: 0 2px 24px rgba(45, 46, 54, 0.06);

  /* --- 排版 --- */
  /* 中文优先栈 */
  --font-serif-cn: "Noto Serif SC", "Source Han Serif SC", "Source Han Serif CN", "Songti SC", "STSongti-SC", "SimSun", serif;
  /* 西文优先混合栈：实现英文数字用 Cormorant，中文自动回退到思源宋体 */
  --font-serif-en: "Cormorant Garamond", "Noto Serif SC", "Source Han Serif SC", "Source Han Serif CN", "Songti SC", serif;
  --font-sans: "Outfit", "PingFang SC", "Microsoft YaHei", sans-serif;
  --font-mono: "DM Mono", "SF Mono", "Fira Code", monospace;

  --fs-hero: clamp(2rem, 5vw, 4.5rem);
  --fs-section-title: clamp(1.5rem, 3.5vw, 3rem);
  --fs-h2: clamp(1.25rem, 2.5vw, 2rem);
  --fs-body: clamp(0.95rem, 1.2vw, 1.1rem);
  --fs-small: clamp(0.75rem, 0.9vw, 0.85rem);
  --fs-nav: 0.85rem;

  --lh-tight: 1.3;
  --lh-body: 1.85;
  --lh-relaxed: 2;

  --ls-wide: 0.15em;
  --ls-ultra: 0.35em;

  /* --- 间距 --- */
  --space-xs: 0.5rem;
  --space-sm: 1rem;
  --space-md: 2rem;
  --space-lg: 4rem;
  --space-xl: 6rem;
  --space-2xl: 10rem;

  /* --- 动效 --- */
  --ease-out-expo: cubic-bezier(0.16, 1, 0.3, 1);
  --ease-out-quart: cubic-bezier(0.25, 1, 0.5, 1);
  --duration-fast: 0.3s;
  --duration-med: 0.6s;
  --duration-slow: 1.2s;

  /* --- 纹理 --- */
  --noise-opacity: 0.03;

  color-scheme: light dark;
}

/* --- 暗黑模式 --- */
[data-theme="dark"] {
  --bg-primary: var(--color-ink);
  --bg-secondary: #22222A;
  --bg-nav: rgba(26, 26, 32, 0.9);
  --text-primary: var(--color-bone);
  --text-secondary: #A8A8B0;
  --text-muted: #6E6E78;
  --accent: var(--color-camellia-dim);
  --border-subtle: rgba(232, 230, 225, 0.06);
  --shadow-soft: 0 2px 24px rgba(0, 0, 0, 0.2);
  --noise-opacity: 0.05;
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg-primary: var(--color-ink);
    --bg-secondary: #22222A;
    --bg-nav: rgba(26, 26, 32, 0.9);
    --text-primary: var(--color-bone);
    --text-secondary: #A8A8B0;
    --text-muted: #6E6E78;
    --accent: var(--color-camellia-dim);
    --border-subtle: rgba(232, 230, 225, 0.06);
    --shadow-soft: 0 2px 24px rgba(0, 0, 0, 0.2);
    --noise-opacity: 0.05;
  }
}

/* ============================================================
   基础重置
   ============================================================ */
*,
*::before,
*::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  font-size: 16px;
}

body {
  font-family: var(--font-serif-cn);
  color: var(--text-primary);
  background-color: var(--bg-primary);
  line-height: var(--lh-body);
  overflow-x: hidden;
  transition: background-color var(--duration-med) var(--ease-out-quart),
    color var(--duration-med) var(--ease-out-quart);
}

/* 宣纸/噪点纹理叠加 */
body::before {
  content: "";
  position: fixed;
  inset: 0;
  pointer-events: none;
  z-index: 9999;
  opacity: var(--noise-opacity);
  background-image: url("data:image/svg+xml,%3Csvg viewBox='0 0 256 256' xmlns='http://www.w3.org/2000/svg'%3E%3Cfilter id='n'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.9' numOctaves='4' stitchTiles='stitch'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23n)'/%3E%3C/svg%3E");
  background-repeat: repeat;
  background-size: 256px 256px;
}

img {
  max-width: 100%;
  height: auto;
  display: block;
}

a {
  color: inherit;
  text-decoration: none;
}

button {
  border: none;
  background: none;
  cursor: pointer;
  font: inherit;
  color: inherit;
}

::selection {
  background-color: var(--accent);
  color: var(--color-rice);
}

/* ============================================================
   导航栏
   ============================================================ */
.site-nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 1000;
  padding: var(--space-sm) var(--space-md);
  display: flex;
  align-items: center;
  justify-content: space-between;
  background: var(--bg-nav);
  backdrop-filter: blur(24px) saturate(1.8);
  -webkit-backdrop-filter: blur(24px) saturate(1.8);
  border-bottom: 1px solid rgba(150, 150, 150, 0.1);
  box-shadow: 0 4px 30px rgba(0, 0, 0, 0.03);
  transition: all var(--duration-fast) var(--ease-out-quart);
}

.nav-logo {
  display: flex;
  align-items: center;
  transition: opacity var(--duration-fast);
}

.nav-logo:hover {
  opacity: 0.8;
}

.logo-svg {
  height: 38px;
  /* 稍微放大一点点：以前是28px */
  width: auto;
  display: block;
  transition: all var(--duration-fast);
}

.logo-accent {
  stroke: var(--accent);
  fill: none !important;
  transition: stroke var(--duration-fast);
}

.logo-text {
  fill: var(--text-primary);
  stroke: none !important;
  transition: fill var(--duration-fast);
}

/* 暗黑模式下变成纯色 #E8E6E1 */
[data-theme="dark"] .logo-accent {
  stroke: var(--color-bone);
}

[data-theme="dark"] .logo-text {
  fill: var(--color-bone);
}

.nav-links {
  display: flex;
  align-items: center;
  gap: var(--space-md);
  list-style: none;
}

.nav-links a {
  font-family: var(--font-sans);
  font-size: var(--fs-nav);
  font-weight: 400;
  letter-spacing: var(--ls-wide);
  text-transform: uppercase;
  color: var(--text-secondary);
  position: relative;
  padding-bottom: 2px;
  transition: color var(--duration-fast);
}

.nav-links a::after {
  content: "";
  position: absolute;
  bottom: -2px;
  left: 0;
  width: 0;
  height: 1.5px;
  background: var(--accent);
  box-shadow: 0 0 8px rgba(238, 63, 77, 0.4);
  transition: width var(--duration-fast) var(--ease-out-expo);
}

.nav-links a:hover {
  color: var(--text-primary);
}

.nav-links a:hover::after {
  width: 100%;
}

.nav-controls {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
}

.btn-lang,
.btn-theme {
  font-family: var(--font-sans);
  font-size: var(--fs-small);
  letter-spacing: var(--ls-wide);
  color: var(--text-muted);
  padding: 0.3em 0.65em;
  border: 1px solid var(--border-subtle);
  border-radius: 4px;
  transition: all var(--duration-fast);
  line-height: 1;
}

.btn-lang:hover,
.btn-theme:hover {
  color: var(--text-primary);
  border-color: var(--accent);
  box-shadow: 0 0 12px rgba(238, 63, 77, 0.15);
}

/* 移除专门给 Emoji 使用的大字号重置，令其与 .btn-lang 一致 */

/* 移动端导航 */
.nav-toggle {
  display: none;
  flex-direction: column;
  gap: 5px;
  padding: 4px;
  cursor: pointer;
}

.nav-toggle span {
  display: block;
  width: 22px;
  height: 1.5px;
  background: var(--text-primary);
  transition: all var(--duration-fast);
}

/* ============================================================
   第一屏：卷首 (Hero)
   ============================================================ */
.section-hero {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  position: relative;
  padding: var(--space-xl) var(--space-md);
  overflow: hidden;
}

/* 背景装饰：极细的水平线 */
.section-hero::before {
  content: "";
  position: absolute;
  top: 50%;
  left: 10%;
  right: 10%;
  height: 1px;
  background: linear-gradient(90deg,
      transparent 0%,
      var(--border-subtle) 20%,
      var(--border-subtle) 80%,
      transparent 100%);
  transform: translateY(-50%);
  opacity: 0.5;
}

.hero-tagline {
  font-family: var(--font-serif-en);
  font-size: var(--fs-hero);
  font-weight: 300;
  letter-spacing: 0.06em;
  text-align: center;
  line-height: var(--lh-tight);
  color: var(--text-primary);
  position: relative;
  z-index: 1;
}

/* 移除强制切换，依靠混合字体栈实现自动匹配 */

.hero-tagline .char {
  display: inline-block;
  opacity: 0;
  transform: translateY(24px);
  animation: charReveal 0.8s var(--ease-out-expo) forwards;
}

@keyframes charReveal {
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.hero-sub {
  font-family: var(--font-sans);
  font-size: var(--fs-small);
  letter-spacing: var(--ls-ultra);
  text-transform: uppercase;
  color: var(--text-muted);
  margin-top: var(--space-lg);
  position: relative;
  z-index: 1;
  opacity: 0;
  animation: fadeUp 1s var(--ease-out-expo) 2s forwards;
}

.hero-scroll-hint {
  position: absolute;
  bottom: var(--space-md);
  left: 0;
  right: 0;
  margin: 0 auto;
  width: max-content;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: var(--space-xs);
  opacity: 0;
  animation: fadeUp 1s var(--ease-out-expo) 2.5s forwards;
}

.hero-scroll-hint span {
  font-family: var(--font-sans);
  font-size: 0.7rem;
  letter-spacing: var(--ls-ultra);
  text-transform: uppercase;
  color: var(--text-muted);
}

.scroll-line {
  width: 1px;
  height: 40px;
  background: linear-gradient(to bottom, var(--accent), transparent);
  animation: scrollPulse 2s ease-in-out infinite;
}

@keyframes scrollPulse {

  0%,
  100% {
    opacity: 0.3;
    transform: scaleY(0.7);
  }

  50% {
    opacity: 1;
    transform: scaleY(1);
  }
}

/* ============================================================
   通用版块样式
   ============================================================ */
.section {
  padding: var(--space-2xl) var(--space-md);
  max-width: 1200px;
  margin: 0 auto;
  position: relative;
}

.section-full {
  max-width: none;
  padding: var(--space-2xl) 0;
}

/* 滚动淡入动效 */
.reveal {
  opacity: 0;
  transform: translateY(30px) scale(0.98);
  filter: blur(4px);
  transition: opacity var(--duration-slow) var(--ease-out-expo),
    transform var(--duration-slow) var(--ease-out-expo),
    filter var(--duration-slow) var(--ease-out-expo);
}

.reveal.visible {
  opacity: 1;
  transform: translateY(0) scale(1);
  filter: blur(0);
}

.reveal-delay-1 {
  transition-delay: 0.15s;
}

.reveal-delay-2 {
  transition-delay: 0.3s;
}

.reveal-delay-3 {
  transition-delay: 0.45s;
}

.reveal-delay-4 {
  transition-delay: 0.6s;
}

/* 版块编号装饰 */
.section-number {
  font-family: var(--font-serif-en);
  font-size: 0.8rem;
  font-weight: 400;
  letter-spacing: var(--ls-ultra);
  color: var(--text-muted);
  margin-bottom: var(--space-sm);
  display: block;
}

.section-label {
  font-family: var(--font-sans);
  font-size: var(--fs-small);
  font-weight: 400;
  letter-spacing: var(--ls-ultra);
  text-transform: uppercase;
  color: var(--text-muted);
  margin-bottom: var(--space-xs);
}

/* ============================================================
   第二屏：溯源 (Origin)
   ============================================================ */
.section-origin {
  display: grid;
  grid-template-columns: 200px 1fr;
  gap: var(--space-xl);
  align-items: start;
  border-top: 1px solid var(--border-subtle);
}

.origin-title-vertical {
  font-family: var(--font-serif-cn);
  font-size: clamp(2.5rem, 5vw, 4rem);
  font-weight: 600;
  writing-mode: vertical-rl;
  text-orientation: mixed;
  letter-spacing: 0.3em;
  color: var(--text-primary);
  position: sticky;
  top: 120px;
  line-height: 1;
}

.origin-content {
  padding-top: var(--space-md);
}

.origin-en-title {
  font-family: var(--font-serif-en);
  font-size: var(--fs-section-title);
  font-weight: 300;
  font-style: italic;
  color: var(--text-muted);
  margin-bottom: var(--space-lg);
  letter-spacing: 0.04em;
}

.origin-text {
  font-size: var(--fs-body);
  line-height: var(--lh-relaxed);
  color: var(--text-secondary);
  max-width: 640px;
}

.origin-text p {
  margin-bottom: var(--space-md);
}

/* 茶花红装饰线 */
.origin-accent-line {
  width: 48px;
  height: 2px;
  background: var(--accent);
  margin: var(--space-lg) 0;
  box-shadow: 0 0 12px rgba(238, 63, 77, 0.3);
}

.origin-quote {
  font-family: var(--font-serif-cn);
  font-size: clamp(1.1rem, 1.5vw, 1.3rem);
  font-weight: 600;
  color: var(--text-primary);
  line-height: var(--lh-body);
  border-left: 2px solid var(--accent);
  padding-left: var(--space-md);
  margin-top: var(--space-lg);
}

/* ============================================================
   第三屏：一帖元气 (VibeOne)
   ============================================================ */
.section-vibeone {
  border-top: 1px solid var(--border-subtle);
}

.vibeone-header {
  text-align: center;
  margin-bottom: var(--space-xl);
}

.vibeone-header .section-label {
  margin-bottom: var(--space-sm);
  /* 微调为 sm，平衡标题的呼吸感 */
}

.vibeone-journal-title {
  font-family: var(--font-serif-cn);
  font-size: clamp(2.5rem, 5vw, 4rem);
  font-weight: 600;
  letter-spacing: 0.08em;
  color: var(--text-primary);
  line-height: 1;
  margin-bottom: var(--space-xs);
  margin-top: var(--space-xs);
}

.vibeone-accent-line {
  width: 48px;
  height: 2px;
  background: var(--accent);
  margin: var(--space-md) auto 0;
  box-shadow: 0 0 12px rgba(238, 63, 77, 0.3);
}

.vibeone-body {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--space-xl);
  align-items: start;
}

.vibeone-info h3 {
  font-family: var(--font-serif-cn);
  font-size: var(--fs-h2);
  font-weight: 600;
  margin-bottom: var(--space-md);
  color: var(--text-primary);
}

.vibeone-desc {
  font-size: var(--fs-body);
  line-height: var(--lh-relaxed);
  color: var(--text-secondary);
  margin-bottom: var(--space-md);
}

.vibeone-tags {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-xs);
  margin-bottom: var(--space-lg);
}

.tag {
  font-family: var(--font-sans);
  font-size: 0.75rem;
  letter-spacing: var(--ls-wide);
  padding: 0.35em 0.9em;
  border: 1px solid var(--border-subtle);
  border-radius: 2px;
  color: var(--text-muted);
  transition: all var(--duration-fast);
}

.tag:hover {
  border-color: var(--accent);
  color: var(--accent);
}

.vibeone-cta-area {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  text-align: center;
  margin-top: 1rem;
}

.qr-wrapper {
  margin-bottom: 1.2rem;
}

.qr-image {
  width: 180px;
  height: 180px;
  border-radius: 4px;
  object-fit: cover;
}

.qr-hint {
  font-family: var(--font-sans);
  font-size: var(--fs-small);
  letter-spacing: var(--ls-wide);
  color: var(--text-muted);
  margin-top: 0;
}



/* ============================================================
   第四屏：实验室 (The Lab — KakaMind)
   ============================================================ */
.section-lab {
  background: var(--color-horn);
  color: var(--color-silver);
  border-top: none;
  padding: var(--space-2xl) var(--space-md);
  position: relative;
  overflow: hidden;
}

[data-theme="dark"] .section-lab {
  background: #14120F;
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) .section-lab {
    background: #14120F;
  }
}

.section-lab .section-number,
.section-lab .section-label {
  color: rgba(241, 240, 237, 0.4);
}

.lab-inner {
  max-width: 1200px;
  margin: 0 auto;
}

.lab-header {
  margin-bottom: var(--space-xl);
}

.lab-brand-name {
  font-family: var(--font-mono);
  font-size: clamp(2rem, 4vw, 3.5rem);
  font-weight: 400;
  letter-spacing: 0.06em;
  color: var(--color-silver);
  margin-bottom: var(--space-xs);
}

.lab-brand-cn {
  font-family: var(--font-serif-cn);
  font-size: var(--fs-h2);
  color: var(--color-coffee);
  letter-spacing: 0.15em;
}

.lab-body {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--space-xl);
  align-items: start;
}

.lab-concept h3 {
  font-family: var(--font-mono);
  font-size: 0.9rem;
  letter-spacing: var(--ls-wide);
  text-transform: uppercase;
  color: var(--color-coffee);
  margin-bottom: var(--space-md);
}

.lab-concept p {
  font-family: var(--font-sans);
  font-size: var(--fs-body);
  line-height: var(--lh-relaxed);
  color: rgba(241, 240, 237, 0.7);
  margin-bottom: var(--space-md);
}

.lab-status {
  display: inline-flex;
  align-items: center;
  gap: var(--space-xs);
  font-family: var(--font-mono);
  font-size: var(--fs-small);
  letter-spacing: var(--ls-wide);
  color: var(--color-coffee);
  margin-top: var(--space-sm);
}

.status-dot {
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: var(--color-coffee);
  animation: blink 2s ease-in-out infinite;
}

@keyframes blink {

  0%,
  100% {
    opacity: 1;
  }

  50% {
    opacity: 0.3;
  }
}

/* 数据卡片 */
.lab-data {
  display: flex;
  flex-direction: column;
  gap: var(--space-md);
}

.data-card {
  padding: var(--space-md);
  border: 1px solid rgba(148, 88, 51, 0.25);
  border-radius: 4px;
  background: rgba(148, 88, 51, 0.05);
  transition: all var(--duration-fast);
}

.data-card:hover {
  border-color: var(--color-coffee);
  background: rgba(148, 88, 51, 0.1);
}

.data-card-label {
  font-family: var(--font-mono);
  font-size: 0.7rem;
  letter-spacing: var(--ls-ultra);
  text-transform: uppercase;
  color: var(--color-coffee);
  margin-bottom: var(--space-xs);
}

.data-card-value {
  font-family: var(--font-mono);
  font-size: clamp(1.5rem, 2.5vw, 2rem);
  font-weight: 500;
  color: var(--color-silver);
}

.data-card-unit {
  font-size: 0.75em;
  color: rgba(241, 240, 237, 0.5);
  margin-left: 0.25em;
}

/* 打字机效果 */
.typewriter {
  overflow: hidden;
  white-space: nowrap;
  border-right: 2px solid var(--color-coffee);
  animation: typing 3s steps(30) forwards, blinkCursor 0.75s step-end infinite;
  max-width: fit-content;
}

@keyframes typing {
  from {
    width: 0;
  }

  to {
    width: 100%;
  }
}

@keyframes blinkCursor {
  50% {
    border-color: transparent;
  }
}

/* App Icon 展示 */
.lab-icon-showcase {
  width: 120px;
  height: 120px;
  border-radius: 24px;
  overflow: hidden;
  margin-top: var(--space-md);
  box-shadow: 0 8px 32px rgba(0, 0, 0, 0.3);
}

.lab-icon-showcase img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  display: block;
}

/* ============================================================
   第五屏：落款 (Colophon)
   ============================================================ */
.section-colophon {
  border-top: 1px solid var(--border-subtle);
  text-align: center;
  padding: var(--space-xl) var(--space-md);
}

.colophon-inner {
  max-width: 640px;
  margin: 0 auto;
}

.colophon-brand {
  font-family: var(--font-serif-cn);
  font-size: var(--fs-section-title);
  font-weight: 600;
  letter-spacing: 0.15em;
  color: var(--text-primary);
  margin-bottom: var(--space-xs);
}

.colophon-tagline {
  font-family: var(--font-sans);
  font-size: var(--fs-small);
  letter-spacing: var(--ls-ultra);
  text-transform: uppercase;
  color: var(--text-muted);
  margin-bottom: var(--space-lg);
}

.colophon-rule {
  width: 32px;
  height: 2px;
  background: var(--accent);
  margin: 0 auto var(--space-lg);
  box-shadow: 0 0 8px rgba(238, 63, 77, 0.3);
}

.colophon-footer {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: center;
  gap: var(--space-sm) var(--space-md);
  font-family: var(--font-sans);
  font-size: var(--fs-small);
  color: var(--text-muted);
}

.colophon-copyright {
  display: flex;
  gap: 0.5em;
  /* 缩减公司名和年份的间距 */
  align-items: center;
}

.footer-sep {
  width: 3px;
  height: 3px;
  background-color: var(--text-muted);
  border-radius: 50%;
  opacity: 0.5;
}

.colophon-footer a,
.colophon-footer span {
  font-size: inherit;
  /* 统一字号 */
}

.colophon-footer a {
  transition: color var(--duration-fast);
}

.colophon-footer a:hover {
  color: var(--accent);
}

.colophon-email {
  font-family: var(--font-mono);
}

/* ============================================================
   通用动画
   ============================================================ */
@keyframes fadeUp {
  from {
    opacity: 0;
    transform: translateY(20px);
  }

  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes fadeIn {
  from {
    opacity: 0;
  }

  to {
    opacity: 1;
  }
}

/* ============================================================
   响应式
   ============================================================ */
@media (max-width: 900px) {
  .section-origin {
    grid-template-columns: 1fr;
    gap: var(--space-md);
  }

  .origin-title-vertical {
    writing-mode: horizontal-tb;
    text-orientation: initial;
    position: static;
    font-size: clamp(2rem, 8vw, 3rem);
    letter-spacing: 0.15em;
  }

  .vibeone-body {
    grid-template-columns: 1fr;
  }

  .lab-body {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 680px) {
  .site-nav {
    padding: var(--space-xs) var(--space-sm);
  }

  .nav-links {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    height: 100vh;
    padding-top: 80px;
    background: var(--bg-nav);
    backdrop-filter: blur(28px) saturate(2);
    -webkit-backdrop-filter: blur(28px) saturate(2);
    flex-direction: column;
    align-items: center;
    justify-content: flex-start;
    gap: var(--space-lg);
    z-index: 999;
    opacity: 0;
    visibility: hidden;
    transform: translateY(-20px);
    transition: all 0.4s var(--ease-out-expo);
  }

  .nav-links.open {
    display: flex;
    opacity: 1;
    visibility: visible;
    transform: translateY(0);
  }

  .nav-links a {
    font-size: 1.2rem;
  }

  .nav-toggle {
    display: flex;
    z-index: 1001;
  }

  .nav-toggle.active span:nth-child(1) {
    transform: rotate(45deg) translate(4.5px, 4.5px);
  }

  .nav-toggle.active span:nth-child(2) {
    opacity: 0;
  }

  .nav-toggle.active span:nth-child(3) {
    transform: rotate(-45deg) translate(4.5px, -4.5px);
  }

  .section {
    padding: var(--space-xl) var(--space-sm);
  }

  .section-full {
    padding: var(--space-xl) 0;
  }

  .section-lab {
    padding: var(--space-xl) var(--space-sm);
  }

  .hero-tagline {
    font-size: clamp(1.5rem, 7vw, 2.5rem);
  }

  .mobile-br {
    display: block;
    content: "";
    margin-top: 0.2em;
  }

  /* 移动端页脚垂直显示 */
  .colophon-footer {
    flex-direction: column;
    gap: var(--space-xs);
  }

  .footer-sep {
    display: none;
    /* 移除分隔点 */
  }
}

/* 桌面端隐藏移动端换行 */
@media (min-width: 681px) {
  .mobile-br {
    display: none;
  }
}

/* ============================================================
   返回顶部悬浮按钮 (Back to Top)
   ============================================================ */
.back-to-top {
  position: fixed;
  bottom: 2.5rem;
  right: 2.5rem;
  width: 46px;
  height: 46px;
  background-color: var(--bg-nav);
  color: var(--text-primary);
  border: 1px solid var(--border-subtle);
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 998;
  cursor: pointer;
  opacity: 0;
  visibility: hidden;
  transform: translateY(20px);
  transition: all var(--duration-med) var(--ease-out-expo);
  box-shadow: var(--shadow-soft);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
}

.back-to-top.visible {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}

.back-to-top:hover {
  background-color: var(--accent);
  color: var(--color-rice);
  border-color: var(--accent);
  transform: translateY(-5px);
  box-shadow: 0 10px 30px rgba(238, 63, 77, 0.25);
}

.back-to-top svg {
  width: 20px;
  height: 20px;
  transition: transform var(--duration-fast);
}

.back-to-top:hover svg {
  animation: bounceUp 0.6s ease-in-out infinite alternate;
}

@keyframes bounceUp {
  from {
    transform: translateY(1px);
  }

  to {
    transform: translateY(-3px);
  }
}

@media (max-width: 680px) {
  .back-to-top {
    bottom: 2rem;
    right: 1.5rem;
    width: 42px;
    height: 42px;
  }
}