/* ============================================
   恋爱双向成长手册 · 精致版样式
   - 深色主题（olxc.art 深夜阅读调性）
   - 上篇粉调（#FF6B9D），下篇橙调（#FFA45C）
   - 响应式 / 流畅动效
   ============================================ */

* { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }

:root {
  --bg-base: #0a0612;
  --bg-deep: #060410;
  --bg-soft: #14101e;
  --text-main: #e9e6f0;
  --text-soft: #a8a3b8;
  --text-dim: #6a6478;
  --line: rgba(255,255,255,0.08);
  --line-strong: rgba(255,255,255,0.16);

  --c-pink: #ff6b9d;
  --c-pink-soft: #ff9ec0;
  --c-pink-glow: rgba(255,107,157,0.35);
  --c-orange: #ffa45c;
  --c-orange-soft: #ffc89c;
  --c-orange-glow: rgba(255,164,92,0.35);
  --c-warn: #f76c6c;

  --maxw: 880px;
  --sidew: 280px;
}

body {
  font-family: 'Noto Serif SC', 'Cormorant Garamond', 'Microsoft YaHei', serif;
  background: var(--bg-base);
  color: var(--text-main);
  line-height: 1.85;
  -webkit-font-smoothing: antialiased;
  overflow-x: hidden;
  min-height: 100vh;
  -webkit-tap-highlight-color: transparent;
  -webkit-touch-callout: none;
}

/* 全局：iOS 点击不放大、不高亮、链接无默认装饰 */
a, button {
  -webkit-tap-highlight-color: transparent !important;
  -webkit-touch-callout: none;
  -webkit-user-select: none;
  user-select: none;
  text-decoration: none;
  outline: none;
  -webkit-appearance: none;
  appearance: none;
}
a:active, button:active {
  opacity: 0.7;
  transform: none !important;
}

/* ========== 背景层 ========== */
.bg-layer {
  position: fixed; inset: 0; z-index: -1; pointer-events: none;
  background:
    radial-gradient(ellipse 80% 50% at 50% 0%, #1a1226 0%, transparent 60%),
    radial-gradient(ellipse 60% 40% at 50% 100%, #0d0820 0%, transparent 60%),
    var(--bg-base);
}

.bg-stars {
  position: absolute; inset: 0;
  background-image:
    radial-gradient(1px 1px at 20% 30%, rgba(255,255,255,0.6), transparent 50%),
    radial-gradient(1px 1px at 40% 70%, rgba(255,255,255,0.5), transparent 50%),
    radial-gradient(1px 1px at 60% 20%, rgba(255,255,255,0.4), transparent 50%),
    radial-gradient(1px 1px at 80% 80%, rgba(255,255,255,0.7), transparent 50%),
    radial-gradient(1.5px 1.5px at 10% 60%, rgba(255,255,255,0.3), transparent 50%),
    radial-gradient(1.5px 1.5px at 90% 40%, rgba(255,255,255,0.4), transparent 50%),
    radial-gradient(2px 2px at 30% 90%, rgba(255,200,180,0.4), transparent 50%),
    radial-gradient(2px 2px at 70% 50%, rgba(180,200,255,0.3), transparent 50%);
  background-size: 600px 600px;
  opacity: 0.7;
  animation: starsDrift 90s linear infinite;
}

@keyframes starsDrift {
  from { background-position: 0 0; }
  to { background-position: 600px 600px; }
}

.bg-glow {
  position: absolute;
  width: 600px; height: 600px;
  border-radius: 50%;
  filter: blur(120px);
  opacity: 0.35;
  transition: opacity 1.5s ease;
}
.bg-glow-pink {
  top: 10%; left: -200px;
  background: var(--c-pink);
}
.bg-glow-orange {
  bottom: 10%; right: -200px;
  background: var(--c-orange);
}

body[data-section="upper"] .bg-glow-pink { opacity: 0.6; }
body[data-section="lower"] .bg-glow-orange { opacity: 0.6; }

.bg-grid {
  position: absolute; inset: 0;
  background-image:
    linear-gradient(rgba(255,255,255,0.025) 1px, transparent 1px),
    linear-gradient(90deg, rgba(255,255,255,0.025) 1px, transparent 1px);
  background-size: 60px 60px;
  mask-image: radial-gradient(ellipse 70% 60% at 50% 50%, black 30%, transparent 80%);
}

/* ========== 顶部导航 ========== */
.topbar {
  position: fixed; top: 0; left: 0; right: 0; z-index: 100;
  background: rgba(10,6,18,0.7);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--line);
  transition: all 0.3s ease;
}
.topbar.scrolled { background: rgba(10,6,18,0.92); }

.topbar-inner {
  max-width: 1200px; margin: 0 auto;
  padding: 14px 28px;
  display: flex; align-items: center; justify-content: space-between;
  gap: 24px;
}
.brand {
  display: flex; align-items: center; gap: 10px;
  text-decoration: none; color: var(--text-main);
  font-weight: 500; font-size: 14px;
  letter-spacing: 0.5px;
}
.brand-mark {
  color: var(--c-pink);
  font-size: 16px;
  filter: drop-shadow(0 0 6px var(--c-pink-glow));
}
.topnav {
  display: flex; gap: 4px; align-items: center;
}
.topnav a {
  color: var(--text-soft);
  text-decoration: none;
  font-size: 13px;
  padding: 6px 14px;
  border-radius: 999px;
  transition: all 0.25s ease;
  letter-spacing: 1px;
}
.topnav a:hover { color: var(--text-main); background: rgba(255,255,255,0.05); }
.topnav a.nav-upper:hover { color: var(--c-pink-soft); background: rgba(255,107,157,0.1); }
.topnav a.nav-lower:hover { color: var(--c-orange-soft); background: rgba(255,164,92,0.1); }

.topbar-actions {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  margin-left: 4px;
}
.topbar-actions a {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  padding: 6px 12px;
  border-radius: 999px;
  font-size: 13px;
  letter-spacing: 1px;
  text-decoration: none;
  transition: all 0.25s ease;
  white-space: nowrap;
}
.topbar-actions a svg {
  flex-shrink: 0;
}
.topbar-actions a.nav-back {
  color: var(--text-soft);
  border: 1px solid var(--line-strong);
  background: rgba(255,255,255,0.02);
}
.topbar-actions a.nav-back:hover {
  color: var(--c-pink-soft);
  border-color: var(--c-pink);
  background: rgba(255,107,157,0.08);
}
.topbar-actions a.nav-download {
  color: var(--text-main);
  border: 1px solid var(--c-pink);
  background: linear-gradient(135deg, rgba(255,107,157,0.18) 0%, rgba(255,164,92,0.18) 100%);
  font-weight: 500;
}
.topbar-actions a.nav-download:hover {
  background: linear-gradient(135deg, rgba(255,107,157,0.30) 0%, rgba(255,164,92,0.30) 100%);
  border-color: var(--c-pink-soft);
  transform: translateY(-1px);
  box-shadow: 0 4px 12px rgba(255,107,157,0.25);
}

.nav-toggle {
  display: none;
  background: none; border: 1px solid var(--line-strong);
  border-radius: 8px;
  width: 38px; height: 38px;
  cursor: pointer;
  flex-direction: column; gap: 4px;
  align-items: center; justify-content: center;
}
.nav-toggle span {
  display: block; width: 18px; height: 1.5px;
  background: var(--text-main);
}

/* ========== 容器 ========== */
.container {
  max-width: var(--maxw);
  margin: 0 auto;
  padding: 0 24px;
}

.section {
  padding: 120px 0 80px;
  position: relative;
}

.section-title {
  font-size: 36px;
  font-weight: 600;
  letter-spacing: 2px;
  background: linear-gradient(120deg, var(--c-pink-soft) 0%, var(--c-orange-soft) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  margin-bottom: 16px;
}

.chapter-tag {
  font-family: 'Cormorant Garamond', serif;
  font-size: 13px;
  letter-spacing: 4px;
  color: var(--text-dim);
  text-transform: uppercase;
  margin-bottom: 8px;
}

.section-divider {
  width: 60px; height: 1px;
  background: linear-gradient(90deg, var(--c-pink) 0%, var(--c-orange) 100%);
  margin: 20px 0 40px;
}

/* ========== 封面 ========== */
.section-cover {
  min-height: 100vh;
  display: flex; align-items: center; justify-content: center;
  padding: 80px 24px;
  position: relative;
}

.cover-frame {
  width: 100%;
  max-width: 1100px;
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  gap: 40px;
  align-items: center;
}

.cover-side {
  position: relative;
  padding: 60px 32px;
  border-radius: 4px;
  text-align: center;
  min-height: 380px;
  display: flex; flex-direction: column; justify-content: center;
}

.cover-upper {
  background: linear-gradient(160deg, rgba(255,107,157,0.10) 0%, rgba(255,107,157,0.02) 100%);
  border: 1px solid rgba(255,107,157,0.25);
  box-shadow:
    inset 0 0 60px rgba(255,107,157,0.05),
    0 0 60px rgba(255,107,157,0.08);
}
.cover-lower {
  background: linear-gradient(200deg, rgba(255,164,92,0.10) 0%, rgba(255,164,92,0.02) 100%);
  border: 1px solid rgba(255,164,92,0.25);
  box-shadow:
    inset 0 0 60px rgba(255,164,92,0.05),
    0 0 60px rgba(255,164,92,0.08);
}

.cover-side-label {
  font-family: 'Cormorant Garamond', serif;
  font-size: 12px;
  letter-spacing: 4px;
  color: var(--text-dim);
  margin-bottom: 24px;
  text-transform: uppercase;
}
.cover-upper .cover-side-label { color: var(--c-pink); }
.cover-lower .cover-side-label { color: var(--c-orange); }

.cover-side-title {
  font-size: 28px;
  font-weight: 600;
  margin-bottom: 12px;
  letter-spacing: 2px;
}
.cover-upper .cover-side-title { color: var(--c-pink-soft); }
.cover-lower .cover-side-title { color: var(--c-orange-soft); }

.cover-side-sub {
  font-size: 13px;
  color: var(--text-soft);
  letter-spacing: 1px;
  line-height: 1.7;
}

.cover-side-arrow {
  margin-top: 28px;
  font-size: 18px;
  color: var(--text-dim);
  letter-spacing: 8px;
  font-family: 'Cormorant Garamond', serif;
}

.cover-center {
  text-align: center;
  padding: 0 20px;
  position: relative;
}

.cover-emblem {
  position: relative;
  width: 120px; height: 120px;
  margin: 0 auto 28px;
  display: flex; align-items: center; justify-content: center;
}

.cover-emblem-ring {
  position: absolute; inset: 0;
  border: 1px solid;
  border-color: var(--c-pink) var(--c-orange) var(--c-orange) var(--c-pink);
  border-radius: 50%;
  animation: ringSpin 16s linear infinite;
}
.cover-emblem-ring-2 {
  inset: 12px;
  border-color: var(--c-orange) var(--c-pink) var(--c-pink) var(--c-orange);
  animation-direction: reverse;
  animation-duration: 22s;
  opacity: 0.6;
}

@keyframes ringSpin {
  from { transform: rotate(0); }
  to { transform: rotate(360deg); }
}

.cover-emblem-core {
  font-size: 32px;
  background: linear-gradient(135deg, var(--c-pink) 0%, var(--c-orange) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  filter: drop-shadow(0 0 12px var(--c-pink-glow));
  animation: corePulse 3s ease-in-out infinite;
}

@keyframes corePulse {
  0%, 100% { transform: scale(1); opacity: 0.9; }
  50% { transform: scale(1.1); opacity: 1; }
}

.cover-main-title {
  font-size: 22px;
  font-weight: 500;
  color: var(--text-main);
  letter-spacing: 6px;
  margin-bottom: 16px;
  writing-mode: horizontal-tb;
}

.cover-meta {
  font-size: 11px;
  color: var(--text-dim);
  letter-spacing: 3px;
  font-family: 'Cormorant Garamond', serif;
}

.cover-bottom {
  position: absolute;
  bottom: 40px; left: 50%;
  transform: translateX(-50%);
  text-align: center;
  display: flex; flex-direction: column; align-items: center; gap: 12px;
}

.cover-cta {
  display: inline-flex; align-items: center; gap: 10px;
  padding: 12px 28px;
  border: 1px solid var(--line-strong);
  border-radius: 999px;
  color: var(--text-main);
  text-decoration: none;
  font-size: 13px;
  letter-spacing: 3px;
  transition: all 0.3s ease;
  background: rgba(255,255,255,0.02);
}
.cover-cta:hover {
  background: rgba(255,255,255,0.06);
  border-color: var(--c-pink);
  color: var(--c-pink-soft);
  transform: translateY(-2px);
}

.cover-scroll-hint {
  font-size: 10px;
  color: var(--text-dim);
  letter-spacing: 4px;
  font-family: 'Cormorant Garamond', serif;
  animation: hintFade 2.5s ease-in-out infinite;
}
@keyframes hintFade {
  0%, 100% { opacity: 0.4; }
  50% { opacity: 1; }
}

/* ========== 序言 ========== */
.section-preface { padding: 100px 0 80px; }

.preface-head {
  text-align: center;
  margin-bottom: 60px;
}
.preface-head .section-divider { margin-left: auto; margin-right: auto; }

.preface-body { font-size: 16px; color: var(--text-soft); }
.preface-body p {
  margin-bottom: 22px;
  text-indent: 2em;
  position: relative;
}
.preface-body p:first-of-type {
  font-size: 18px;
  color: var(--text-main);
  font-weight: 500;
  text-indent: 0;
  text-align: center;
  padding: 30px 0;
  border-top: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
  background: linear-gradient(90deg, transparent, rgba(255,107,157,0.05), transparent);
}

/* ========== 上下篇 ========== */
.section-part { padding: 80px 0; }

.part-hero {
  padding: 100px 0 80px;
  text-align: center;
  position: relative;
}
.part-hero::before {
  content: '';
  position: absolute; inset: 0;
  pointer-events: none;
  background: radial-gradient(ellipse 60% 40% at 50% 50%, var(--glow-color, transparent) 0%, transparent 70%);
  opacity: 0.5;
}
[data-section="upper"] .part-hero { --glow-color: var(--c-pink-glow); }
[data-section="lower"] .part-hero { --glow-color: var(--c-orange-glow); }

.part-tag {
  font-family: 'Cormorant Garamond', serif;
  font-size: 12px;
  letter-spacing: 6px;
  text-transform: uppercase;
  margin-bottom: 16px;
  color: var(--text-dim);
}
[data-section="upper"] .part-tag { color: var(--c-pink); }
[data-section="lower"] .part-tag { color: var(--c-orange); }

.part-title {
  font-size: 56px;
  font-weight: 600;
  letter-spacing: 6px;
  margin-bottom: 20px;
  line-height: 1.2;
}
[data-section="upper"] .part-title {
  background: linear-gradient(120deg, var(--c-pink) 0%, var(--c-pink-soft) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  filter: drop-shadow(0 0 20px var(--c-pink-glow));
}
[data-section="lower"] .part-title {
  background: linear-gradient(120deg, var(--c-orange) 0%, var(--c-orange-soft) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  filter: drop-shadow(0 0 20px var(--c-orange-glow));
}

.part-subtitle {
  font-size: 15px;
  color: var(--text-soft);
  letter-spacing: 2px;
  margin-bottom: 24px;
}

.part-meta {
  display: inline-flex;
  align-items: center; gap: 16px;
  padding: 8px 20px;
  border: 1px solid var(--line);
  border-radius: 999px;
  font-size: 12px;
  color: var(--text-dim);
  letter-spacing: 2px;
}
[data-section="upper"] .part-meta { border-color: rgba(255,107,157,0.3); color: var(--c-pink-soft); }
[data-section="lower"] .part-meta { border-color: rgba(255,164,92,0.3); color: var(--c-orange-soft); }
.part-meta-item { display: flex; align-items: center; gap: 4px; }
.part-meta-item + .part-meta-item::before {
  content: '·';
  margin-right: 16px;
  color: var(--text-dim);
}

/* ========== 引言卡 ========== */
.intro-card {
  margin: 60px 0;
  padding: 40px;
  background: rgba(255,255,255,0.02);
  border-radius: 8px;
  border: 1px solid var(--line);
  position: relative;
  overflow: hidden;
}
[data-section="upper"] .intro-card { border-left: 3px solid var(--c-pink); }
[data-section="lower"] .intro-card { border-left: 3px solid var(--c-orange); }
.intro-card::before {
  content: '';
  position: absolute; inset: 0;
  pointer-events: none;
}
[data-section="upper"] .intro-card::before {
  background: radial-gradient(ellipse at top left, var(--c-pink-glow) 0%, transparent 50%);
  opacity: 0.15;
}
[data-section="lower"] .intro-card::before {
  background: radial-gradient(ellipse at top left, var(--c-orange-glow) 0%, transparent 50%);
  opacity: 0.15;
}

.intro-tag {
  display: inline-block;
  font-family: 'Cormorant Garamond', serif;
  font-size: 12px;
  letter-spacing: 4px;
  text-transform: uppercase;
  margin-bottom: 24px;
  padding: 4px 14px;
  border-radius: 4px;
}
[data-section="upper"] .intro-tag { color: var(--c-pink); background: rgba(255,107,157,0.1); }
[data-section="lower"] .intro-tag { color: var(--c-orange); background: rgba(255,164,92,0.1); }

.intro-body p {
  font-size: 15.5px;
  color: var(--text-soft);
  margin-bottom: 18px;
  line-height: 2;
}
.intro-body p strong { color: var(--text-main); font-weight: 600; }

/* ========== 章节 ========== */
.chapters { margin-top: 80px; }

.chapter {
  margin-bottom: 100px;
  padding-top: 40px;
  border-top: 1px solid var(--line);
}
.chapter:first-child { border-top: none; padding-top: 0; }

.chapter-head {
  margin-bottom: 36px;
  position: relative;
}
.chapter-num {
  font-family: 'Cormorant Garamond', serif;
  font-size: 14px;
  letter-spacing: 4px;
  color: var(--text-dim);
  margin-bottom: 12px;
}
[data-section="upper"] .chapter-num { color: var(--c-pink); }
[data-section="lower"] .chapter-num { color: var(--c-orange); }

.chapter-title {
  font-size: 32px;
  font-weight: 600;
  color: var(--text-main);
  margin-bottom: 16px;
  line-height: 1.3;
  position: relative;
  display: inline-block;
}
.chapter-title::after {
  content: '';
  position: absolute;
  bottom: -8px; left: 0;
  width: 48px; height: 2px;
}
[data-section="upper"] .chapter-title::after { background: var(--c-pink); }
[data-section="lower"] .chapter-title::after { background: var(--c-orange); }

.chapter-intro {
  font-size: 15px;
  color: var(--text-soft);
  line-height: 1.95;
  margin-bottom: 36px;
  padding: 20px 24px;
  background: rgba(255,255,255,0.02);
  border-radius: 4px;
  border-left: 2px solid;
}
[data-section="upper"] .chapter-intro { border-left-color: var(--c-pink); }
[data-section="lower"] .chapter-intro { border-left-color: var(--c-orange); }

.blocks { display: flex; flex-direction: column; gap: 18px; }

.block-h3 {
  font-size: 18px;
  font-weight: 600;
  color: var(--text-main);
  margin-top: 24px;
  margin-bottom: 8px;
  padding-left: 14px;
  border-left: 3px solid;
}
[data-section="upper"] .block-h3 { border-left-color: var(--c-pink); }
[data-section="lower"] .block-h3 { border-left-color: var(--c-orange); }

.block-p {
  font-size: 15px;
  color: var(--text-soft);
  line-height: 1.95;
}

.block-warn {
  padding: 16px 20px;
  border-radius: 6px;
  background: rgba(247,108,108,0.08);
  border: 1px solid rgba(247,108,108,0.25);
  border-left: 3px solid var(--c-warn);
  color: #f0a8a8;
  font-size: 14px;
  line-height: 1.85;
  position: relative;
}
.block-warn::before {
  content: '⚠';
  position: absolute;
  left: -14px; top: 16px;
  width: 24px; height: 24px;
  background: var(--c-warn);
  color: white;
  border-radius: 50%;
  display: flex; align-items: center; justify-content: center;
  font-size: 13px;
  font-weight: bold;
}
.block-warn { padding-left: 36px; }

.block-quote {
  text-align: center;
  font-size: 20px;
  font-weight: 500;
  color: var(--text-main);
  padding: 32px 24px;
  font-style: italic;
  font-family: 'Cormorant Garamond', serif;
  position: relative;
  letter-spacing: 1px;
}
[data-section="upper"] .block-quote {
  background: linear-gradient(90deg, transparent, rgba(255,107,157,0.08), transparent);
  color: var(--c-pink-soft);
}
[data-section="lower"] .block-quote {
  background: linear-gradient(90deg, transparent, rgba(255,164,92,0.08), transparent);
  color: var(--c-orange-soft);
}

.block-list {
  position: relative;
  padding-left: 28px;
  color: var(--text-soft);
  font-size: 15px;
  line-height: 1.95;
}
.block-list::before {
  content: '◆';
  position: absolute;
  left: 0; top: 4px;
  font-size: 10px;
}
[data-section="upper"] .block-list::before { color: var(--c-pink); }
[data-section="lower"] .block-list::before { color: var(--c-orange); }

.block-ending {
  text-align: center;
  padding: 60px 20px;
  font-family: 'Cormorant Garamond', serif;
  font-size: 28px;
  color: var(--text-dim);
  letter-spacing: 8px;
}
[data-section="upper"] .block-ending { color: var(--c-pink-soft); }
[data-section="lower"] .block-ending { color: var(--c-orange-soft); }

/* ========== 封底 ========== */
.section-back {
  min-height: 70vh;
  display: flex; align-items: center; justify-content: center;
  text-align: center;
  padding: 120px 24px;
  background:
    radial-gradient(ellipse 50% 40% at 50% 50%, rgba(255,107,157,0.08) 0%, transparent 60%),
    radial-gradient(ellipse 50% 40% at 50% 80%, rgba(255,164,92,0.08) 0%, transparent 60%);
}

.back-inner { max-width: 600px; }

.back-emblem {
  display: flex; align-items: center; justify-content: center; gap: 20px;
  margin-bottom: 40px;
}
.back-emblem-line {
  width: 80px; height: 1px;
  background: linear-gradient(90deg, transparent, var(--c-pink) 50%, var(--c-orange));
}
.back-emblem-dot {
  font-size: 16px;
  background: linear-gradient(135deg, var(--c-pink), var(--c-orange));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  filter: drop-shadow(0 0 8px var(--c-pink-glow));
}

.back-title {
  font-size: 36px;
  font-weight: 500;
  letter-spacing: 8px;
  margin-bottom: 32px;
  color: var(--text-main);
  font-family: 'Cormorant Garamond', serif;
}

.back-quote {
  font-size: 17px;
  line-height: 2;
  color: var(--text-soft);
  margin-bottom: 40px;
  letter-spacing: 2px;
}

.back-sig {
  font-size: 13px;
  letter-spacing: 6px;
  color: var(--text-dim);
  margin-bottom: 60px;
  font-family: 'Cormorant Garamond', serif;
}

.back-meta {
  font-size: 12px;
  color: var(--text-dim);
  line-height: 2;
  letter-spacing: 2px;
  margin-bottom: 50px;
}

.back-top {
  display: inline-flex; align-items: center; gap: 8px;
  padding: 10px 24px;
  border: 1px solid var(--line-strong);
  border-radius: 999px;
  color: var(--text-soft);
  text-decoration: none;
  font-size: 12px;
  letter-spacing: 3px;
  transition: all 0.3s ease;
}
.back-top:hover {
  color: var(--text-main);
  border-color: var(--c-pink);
  transform: translateY(-2px);
}

/* ========== 浮动按钮 ========== */
.float-btns {
  position: fixed; right: 24px; bottom: 24px; z-index: 90;
  display: flex; flex-direction: column; gap: 10px;
}
.float-btn {
  width: 44px; height: 44px;
  background: rgba(20,16,30,0.85);
  backdrop-filter: blur(10px);
  border: 1px solid var(--line-strong);
  border-radius: 50%;
  color: var(--text-soft);
  cursor: pointer;
  display: flex; align-items: center; justify-content: center;
  transition: all 0.25s ease;
}
.float-btn:hover {
  color: var(--c-pink-soft);
  border-color: var(--c-pink);
  background: rgba(255,107,157,0.1);
  transform: translateY(-2px);
}
#btnTop { opacity: 0; pointer-events: none; transition: all 0.3s ease; }
#btnTop.visible { opacity: 1; pointer-events: auto; }

/* ========== 侧边栏 ========== */
.sidebar {
  position: fixed; top: 0; right: 0; bottom: 0;
  width: var(--sidew);
  background: rgba(10,6,18,0.96);
  backdrop-filter: blur(20px);
  border-left: 1px solid var(--line);
  z-index: 200;
  transform: translateX(100%);
  transition: transform 0.3s ease;
  overflow-y: auto;
  padding: 20px 0;
}
.sidebar.open { transform: translateX(0); }

.sidebar-header {
  display: flex; align-items: center; justify-content: space-between;
  padding: 0 20px 16px;
  border-bottom: 1px solid var(--line);
  margin-bottom: 12px;
}
.sidebar-title {
  font-size: 13px;
  letter-spacing: 4px;
  color: var(--text-dim);
  font-family: 'Cormorant Garamond', serif;
  text-transform: uppercase;
}
.sidebar-close {
  background: none; border: none;
  color: var(--text-soft);
  font-size: 24px;
  cursor: pointer;
  width: 32px; height: 32px;
  display: flex; align-items: center; justify-content: center;
  border-radius: 6px;
}
.sidebar-close:hover { background: rgba(255,255,255,0.05); }

.sidebar-nav {
  display: flex; flex-direction: column;
  padding: 0 12px;
}
.sidebar-group {
  margin-bottom: 8px;
}
.sidebar-group-label {
  font-size: 11px;
  letter-spacing: 3px;
  padding: 12px 8px 4px;
  text-transform: uppercase;
}
.sidebar-group[data-part="upper"] .sidebar-group-label { color: var(--c-pink); }
.sidebar-group[data-part="lower"] .sidebar-group-label { color: var(--c-orange); }

.sidebar-link {
  display: block;
  padding: 8px 12px;
  color: var(--text-soft);
  text-decoration: none;
  font-size: 13px;
  border-radius: 4px;
  transition: all 0.2s ease;
  border-left: 2px solid transparent;
}
.sidebar-link:hover {
  background: rgba(255,255,255,0.04);
  color: var(--text-main);
}
.sidebar-group[data-part="upper"] .sidebar-link:hover {
  color: var(--c-pink-soft);
  border-left-color: var(--c-pink);
}
.sidebar-group[data-part="lower"] .sidebar-link:hover {
  color: var(--c-orange-soft);
  border-left-color: var(--c-orange);
}
.sidebar-link.active {
  background: rgba(255,255,255,0.06);
  color: var(--text-main);
  font-weight: 500;
}
.sidebar-group[data-part="upper"] .sidebar-link.active {
  color: var(--c-pink-soft);
  border-left-color: var(--c-pink);
}
.sidebar-group[data-part="lower"] .sidebar-link.active {
  color: var(--c-orange-soft);
  border-left-color: var(--c-orange);
}

/* ========== 滚动入场动画 ========== */
.reveal {
  opacity: 0;
  transform: translateY(30px);
  transition: opacity 0.8s ease, transform 0.8s ease;
}
.reveal.in {
  opacity: 1;
  transform: translateY(0);
}

/* ========== 响应式 ========== */
@media (max-width: 900px) {
  .cover-frame {
    grid-template-columns: 1fr;
    gap: 24px;
  }
  .cover-side { min-height: auto; padding: 40px 24px; }
  .cover-side-arrow { display: none; }
  .cover-center { padding: 20px 0; }
  .cover-main-title { font-size: 18px; letter-spacing: 4px; }
  .cover-emblem { width: 90px; height: 90px; margin-bottom: 20px; }
  .part-title { font-size: 40px; }
  .chapter-title { font-size: 26px; }
  .section { padding: 80px 0 60px; }
  .section-title { font-size: 28px; }
  .topnav { display: none; }
  .topbar-actions { display: inline-flex !important; }
  .topbar-actions a span { display: none; }
  .topbar-actions a { padding: 6px 9px; }
  .nav-toggle { display: flex; }
}

@media (max-width: 600px) {
  .container { padding: 0 18px; }
  .cover-side-title { font-size: 22px; }
  .cover-side-sub { font-size: 12px; }
  .part-title { font-size: 32px; letter-spacing: 4px; }
  .part-subtitle { font-size: 13px; }
  .chapter-title { font-size: 22px; }
  .chapter-intro { padding: 16px 18px; }
  .intro-card { padding: 24px 20px; }
  .preface-body { font-size: 15px; }
  .preface-body p { text-indent: 1.5em; }
  .block-p { font-size: 14.5px; }
  .float-btns { right: 16px; bottom: 16px; }
  .float-btn { width: 40px; height: 40px; }
  .sidebar { width: 100%; }
}

/* ========== 减少动效偏好 ========== */
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    transition-duration: 0.01ms !important;
  }
}