/* === 基础重置与字体 === */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

:root {
  --paper-bg: #f5f0e6;
  --paper-dark: #e8e0d0;
  --ink: #2c1810;
  --ink-light: #5c4030;
  --seal-red: #8b2500;
  --seal-dark: #5c1800;
  --gold: #c9a96e;
  --line: #d4c8b0;
}

html {
  scroll-behavior: smooth;
}

body {
  font-family: "Noto Serif SC", "Songti SC", "SimSun", serif;
  background: var(--paper-bg);
  color: var(--ink);
  line-height: 1.9;
  min-height: 100vh;
  overflow-x: hidden;
}

/* === 纸张纹理背景 === */
body::before {
  content: "";
  position: fixed;
  inset: 0;
  background-image:
    url("data:image/svg+xml,%3Csvg width='200' height='200' viewBox='0 0 200 200' xmlns='http://www.w3.org/2000/svg'%3E%3Cfilter id='noise'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.65' numOctaves='3' stitchTiles='stitch'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23noise)' opacity='0.04'/%3E%3C/svg%3E");
  pointer-events: none;
  z-index: 0;
}

/* === 首页：信的入口 === */
.hero {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 60px 20px;
  position: relative;
}

.letter-envelope {
  width: 100%;
  max-width: 720px;
  background: linear-gradient(135deg, #faf6ee 0%, #f0eadd 100%);
  border: 1px solid var(--line);
  border-radius: 4px;
  padding: 48px 40px 56px;
  position: relative;
  box-shadow:
    0 1px 2px rgba(0,0,0,0.04),
    0 4px 12px rgba(0,0,0,0.06),
    0 16px 48px rgba(0,0,0,0.08);
  transform: rotate(-0.3deg);
  transition: transform 0.6s ease, box-shadow 0.6s ease;
}

.letter-envelope:hover {
  transform: rotate(0deg) translateY(-4px);
  box-shadow:
    0 1px 2px rgba(0,0,0,0.04),
    0 8px 24px rgba(0,0,0,0.08),
    0 24px 64px rgba(0,0,0,0.10);
}

/* 火漆印章 */
.wax-seal {
  width: 72px;
  height: 72px;
  background: radial-gradient(circle at 35% 35%, #a52a00, var(--seal-red));
  border-radius: 50%;
  margin: 0 auto 32px;
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow:
    inset -2px -2px 6px rgba(0,0,0,0.2),
    inset 2px 2px 6px rgba(255,255,255,0.1),
    0 3px 8px rgba(139,37,0,0.3);
  position: relative;
}

.wax-seal::after {
  content: "情";
  font-family: "Kaiti SC", "KaiTi", serif;
  font-size: 28px;
  color: rgba(255,255,255,0.85);
  font-weight: bold;
}

/* 首页标题 */
.hero-title {
  font-family: "Kaiti SC", "KaiTi", serif;
  font-size: 2.4rem;
  text-align: center;
  margin-bottom: 12px;
  color: var(--ink);
  letter-spacing: 0.15em;
}

.hero-subtitle {
  text-align: center;
  font-size: 1rem;
  color: var(--ink-light);
  margin-bottom: 40px;
  letter-spacing: 0.1em;
}

.hero-quote {
  text-align: center;
  font-size: 0.95rem;
  color: var(--ink-light);
  font-style: italic;
  max-width: 480px;
  margin: 0 auto 48px;
  line-height: 2;
  border-top: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
  padding: 20px 0;
}

/* === 导航：三封信 === */
.nav-letters {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 24px;
  max-width: 680px;
  margin: 0 auto;
}

.nav-letter {
  display: block;
  background: linear-gradient(135deg, #fdfbf7 0%, #f5f0e6 100%);
  border: 1px solid var(--line);
  border-radius: 6px;
  padding: 28px 24px;
  text-decoration: none;
  color: var(--ink);
  transition: all 0.4s ease;
  position: relative;
  text-align: center;
}

.nav-letter::before {
  content: "";
  position: absolute;
  top: 12px;
  right: 12px;
  width: 16px;
  height: 16px;
  background: var(--seal-red);
  border-radius: 50%;
  opacity: 0;
  transform: scale(0);
  transition: all 0.4s ease;
}

.nav-letter:hover {
  transform: translateY(-3px);
  box-shadow: 0 8px 24px rgba(0,0,0,0.08);
  border-color: var(--seal-red);
}

.nav-letter:hover::before {
  opacity: 1;
  transform: scale(1);
}

.nav-letter-number {
  font-size: 0.8rem;
  color: var(--seal-red);
  letter-spacing: 0.15em;
  margin-bottom: 8px;
}

.nav-letter-title {
  font-family: "Kaiti SC", "KaiTi", serif;
  font-size: 1.5rem;
  margin-bottom: 8px;
}

.nav-letter-desc {
  font-size: 0.85rem;
  color: var(--ink-light);
  line-height: 1.7;
}

/* === 展厅通用布局 === */
.page-header {
  text-align: center;
  padding: 60px 20px 40px;
}

.page-header .wax-seal {
  width: 48px;
  height: 48px;
  margin-bottom: 20px;
}

.page-header .wax-seal::after {
  font-size: 20px;
}

.page-header h1 {
  font-family: "Kaiti SC", "KaiTi", serif;
  font-size: 2rem;
  letter-spacing: 0.12em;
  margin-bottom: 8px;
}

.page-header p {
  color: var(--ink-light);
  font-size: 0.9rem;
}

/* === 内容容器 === */
.content {
  max-width: 720px;
  margin: 0 auto;
  padding: 0 24px 80px;
  position: relative;
  z-index: 1;
}

/* === 时间线（展厅二） === */
.timeline {
  position: relative;
  padding-left: 32px;
}

.timeline::before {
  content: "";
  position: absolute;
  left: 6px;
  top: 0;
  bottom: 0;
  width: 2px;
  background: linear-gradient(to bottom, var(--seal-red), var(--gold));
}

.timeline-item {
  position: relative;
  margin-bottom: 32px;
  padding-left: 24px;
}

.timeline-item::before {
  content: "";
  position: absolute;
  left: -28px;
  top: 6px;
  width: 10px;
  height: 10px;
  background: var(--seal-red);
  border-radius: 50%;
  border: 2px solid var(--paper-bg);
  box-shadow: 0 0 0 2px var(--seal-red);
}

.timeline-year {
  font-family: "Kaiti SC", "KaiTi", serif;
  font-size: 1.1rem;
  color: var(--seal-red);
  margin-bottom: 4px;
}

.timeline-text {
  color: var(--ink-light);
  font-size: 0.9rem;
  line-height: 1.8;
}

/* === 展柜卡片 === */
.card {
  background: linear-gradient(135deg, #fdfbf7 0%, #f5f0e6 100%);
  border: 1px solid var(--line);
  border-radius: 6px;
  padding: 28px 28px 24px;
  margin-bottom: 24px;
  position: relative;
  transition: all 0.3s ease;
}

.card:hover {
  box-shadow: 0 4px 16px rgba(0,0,0,0.06);
}

.card-title {
  font-family: "Kaiti SC", "KaiTi", serif;
  font-size: 1.2rem;
  color: var(--ink);
  margin-bottom: 4px;
  display: flex;
  align-items: center;
  gap: 10px;
}

.card-title::before {
  content: "";
  width: 6px;
  height: 6px;
  background: var(--seal-red);
  border-radius: 50%;
  display: block;
  flex-shrink: 0;
}

.card-subtitle {
  font-size: 0.8rem;
  color: var(--seal-red);
  margin-bottom: 14px;
  letter-spacing: 0.05em;
}

.card-body {
  color: var(--ink-light);
  font-size: 0.9rem;
  line-height: 2;
}

.card-body p {
  margin-bottom: 12px;
}

/* 引用样式 */
.quote {
  border-left: 3px solid var(--seal-red);
  padding-left: 16px;
  margin: 16px 0;
  color: var(--ink);
  font-style: italic;
}

/* === 可展开内容 === */
.expandable {
  border-top: 1px dashed var(--line);
  margin-top: 16px;
  padding-top: 16px;
}

.expand-toggle {
  display: flex;
  align-items: center;
  gap: 8px;
  cursor: pointer;
  color: var(--seal-red);
  font-size: 0.85rem;
  user-select: none;
  padding: 8px 0;
}

.expand-toggle:hover {
  opacity: 0.8;
}

.expand-icon {
  transition: transform 0.3s ease;
  font-size: 0.7rem;
}

.expand-toggle.open .expand-icon {
  transform: rotate(90deg);
}

.expand-content {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.5s ease, opacity 0.4s ease;
  opacity: 0;
}

.expand-content.open {
  max-height: 2000px;
  opacity: 1;
  margin-top: 12px;
}

/* === 展厅三：信笺 === */
.letter-showcase {
  background: linear-gradient(135deg, #faf6ee 0%, #f0eadd 100%);
  border: 1px solid var(--line);
  border-radius: 6px;
  padding: 32px 28px;
  margin-bottom: 32px;
  position: relative;
  box-shadow: 0 2px 8px rgba(0,0,0,0.04);
}

.letter-showcase::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 4px;
  background: linear-gradient(90deg, var(--seal-red), var(--gold), var(--seal-red));
  opacity: 0.3;
}

.letter-label {
  font-size: 0.75rem;
  color: var(--seal-red);
  letter-spacing: 0.15em;
  text-transform: uppercase;
  margin-bottom: 16px;
  display: flex;
  align-items: center;
  gap: 8px;
}

.letter-label::after {
  content: "";
  flex: 1;
  height: 1px;
  background: var(--line);
}

/* === 信笺正文 === */
.letter-text {
  font-family: "Kaiti SC", "KaiTi", serif;
  font-size: 1.05rem;
  line-height: 2.2;
  color: var(--ink);
  margin-bottom: 20px;
  background: linear-gradient(135deg, #fdfbf7 0%, #f5f0e6 100%);
  border: 1px solid var(--line);
  border-radius: 4px;
  padding: 20px 24px;
  box-shadow: 0 1px 3px rgba(0,0,0,0.04);
}

/* 多封信连续展示时的分隔 */
.letter-text + .letter-text {
  margin-top: 28px;
  padding-top: 24px;
  border-top: 1px dashed var(--line);
}

/* 信内落款 */
.letter-signature {
  display: block;
  text-align: right;
  margin-top: 16px;
  font-size: 1rem;
  color: var(--ink-light);
  letter-spacing: 0.05em;
}

/* 多封信标签（如【第一封】【第二封】） */
.letter-text strong:first-child {
  display: inline-block;
  font-family: "Noto Serif SC", "Songti SC", serif;
  font-size: 0.85rem;
  color: var(--seal-red);
  letter-spacing: 0.1em;
  margin-bottom: 12px;
}

/* 展开内容区内部间距优化 */
.expand-content .letter-text:last-child {
  margin-bottom: 8px;
}

/* === 返回按钮 === */
.back-link {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  color: var(--ink-light);
  text-decoration: none;
  font-size: 0.85rem;
  margin-bottom: 20px;
  transition: color 0.3s;
}

.back-link:hover {
  color: var(--seal-red);
}

.next-hall {
  text-align: center;
  margin: 40px 0 24px;
}

.next-hall .back-link {
  display: inline-flex;
  font-size: 1rem;
  gap: 8px;
}

/* === 页脚 === */
.footer {
  text-align: center;
  padding: 40px 20px;
  color: var(--ink-light);
  font-size: 0.8rem;
  border-top: 1px solid var(--line);
  margin-top: 40px;
}

.footer-note {
  margin-top: 4px;
  opacity: 0.6;
}

.js-fade {
  opacity: 0;
  transform: translateY(16px);
  transition: opacity 0.6s ease, transform 0.6s ease;
}

.js-fade.is-visible {
  opacity: 1;
  transform: translateY(0);
}

/* === 返回顶部 === */
.back-to-top {
  position: fixed;
  right: 20px;
  bottom: 24px;
  width: 44px;
  height: 44px;
  border-radius: 50%;
  background: var(--seal-red);
  color: #fff;
  border: none;
  font-size: 1.2rem;
  cursor: pointer;
  opacity: 0;
  transform: translateY(12px);
  transition: opacity 0.4s ease, transform 0.4s ease;
  z-index: 100;
  box-shadow: 0 2px 8px rgba(139,37,0,0.3);
}

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

/* === 展厅五：锚点目录 === */
.toc-letters {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-bottom: 24px;
}

.toc-letters a {
  display: inline-block;
  padding: 6px 12px;
  background: linear-gradient(135deg, #fdfbf7 0%, #f5f0e6 100%);
  border: 1px solid var(--line);
  border-radius: 4px;
  color: var(--ink-light);
  text-decoration: none;
  font-size: 0.8rem;
  transition: all 0.3s ease;
}

.toc-letters a:hover {
  border-color: var(--seal-red);
  color: var(--seal-red);
}

/* === 动画 === */
@keyframes fadeInUp {
  from {
    opacity: 0;
    transform: translateY(20px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.fade-in {
  animation: fadeInUp 0.8s ease forwards;
}

.fade-in-delay-1 { animation-delay: 0.1s; }
.fade-in-delay-2 { animation-delay: 0.2s; }
.fade-in-delay-3 { animation-delay: 0.3s; }
.fade-in-delay-4 { animation-delay: 0.4s; }

/* === 分隔线 === */
.divider {
  text-align: center;
  margin: 40px 0;
  position: relative;
}

.divider::before {
  content: "";
  position: absolute;
  top: 50%;
  left: 0;
  right: 0;
  height: 1px;
  background: var(--line);
}

.divider span {
  display: inline-block;
  background: var(--paper-bg);
  padding: 0 16px;
  position: relative;
  color: var(--seal-red);
  font-size: 0.8rem;
  letter-spacing: 0.2em;
}

/* === 响应式 === */
@media (max-width: 640px) {
  .hero-title {
    font-size: 1.8rem;
  }
  .letter-envelope {
    padding: 32px 24px;
  }
  .content {
    padding: 0 16px 60px;
  }
}

/* 移动端时间线优化 */
@media (max-width: 640px) {
  .timeline {
    padding-left: 20px;
  }
  .timeline::before {
    left: 4px;
  }
  .timeline-item {
    padding-left: 16px;
  }
  .timeline-item::before {
    left: -20px;
    width: 8px;
    height: 8px;
  }
  .back-to-top {
    right: 12px;
    bottom: 16px;
    width: 40px;
    height: 40px;
    font-size: 1rem;
  }
}

/* 打印优化 */
@media print {
  body {
    background: white;
  }
  body::before {
    display: none;
  }
}