* {
  box-sizing: border-box;
}

:root {
  --bg: #f6f4ef;
  --panel: #ffffff;
  --text: #1f2937;
  --muted: #667085;
  --border: #e5e7eb;
  --accent: #2f6f4e;
  --accent-soft: #e7f1ea;
  --shadow: 0 20px 60px rgba(31, 41, 55, 0.08);
  --radius: 18px;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  font-family: ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  color: var(--text);
  background:
    radial-gradient(circle at top left, rgba(47, 111, 78, 0.08), transparent 28%),
    linear-gradient(180deg, #fbfaf7 0%, var(--bg) 100%);
}

a {
  color: inherit;
}

.book-shell {
  display: grid;
  grid-template-columns: 320px minmax(0, 1fr);
  min-height: 100vh;
}

.book-sidebar {
  position: sticky;
  top: 0;
  align-self: start;
  height: 100vh;
  overflow: auto;
  padding: 2rem 1.25rem;
  border-right: 1px solid var(--border);
  background: rgba(246, 244, 239, 0.88);
  backdrop-filter: blur(14px);
}

.book-brand {
  padding: 1rem 1rem 1.5rem;
  margin-bottom: 1rem;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--panel);
  box-shadow: var(--shadow);
}

.book-title {
  display: block;
  font-size: 1.4rem;
  font-weight: 800;
  text-decoration: none;
}

.book-title:hover {
  color: var(--accent);
}

.book-subtitle {
  margin: 0.5rem 0 0;
  color: var(--muted);
  font-size: 0.92rem;
}

.book-nav-group {
  margin-top: 1.25rem;
}

.book-nav-group h2,
.book-page-header h1,
.book-article-header h1 {
  margin: 0;
  line-height: 1.2;
}

.book-nav-group h2 {
  margin-bottom: 0.75rem;
  font-size: 0.8rem;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--muted);
}

.book-nav-group ul {
  list-style: none;
  padding: 0;
  margin: 0;
}

.book-nav-group li + li {
  margin-top: 0.35rem;
}

.book-nav-group a {
  display: block;
  padding: 0.6rem 0.8rem;
  border-radius: 12px;
  color: var(--text);
  text-decoration: none;
}

.book-nav-group a:hover,
.book-nav-group a.active {
  background: var(--accent-soft);
  color: var(--accent);
}

.book-main {
  min-width: 0;
}

.book-topbar {
  display: none;
  align-items: center;
  gap: 1rem;
  padding: 1rem 1.25rem;
  border-bottom: 1px solid var(--border);
  background: rgba(251, 250, 247, 0.92);
  backdrop-filter: blur(12px);
}

.book-toggle {
  border: 1px solid var(--border);
  border-radius: 999px;
  padding: 0.55rem 0.9rem;
  background: var(--panel);
  color: var(--text);
}

.book-topbar-title {
  font-weight: 700;
}

.book-content {
  max-width: 980px;
  padding: 2.5rem 3rem 4rem;
}

.book-page-header,
.book-article-header {
  margin-bottom: 1.5rem;
}

.book-kicker {
  margin: 0 0 0.75rem;
  font-size: 0.82rem;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--accent);
  font-weight: 700;
}

.book-page-header h1,
.book-article-header h1 {
  font-size: clamp(2rem, 4vw, 3.1rem);
}

.book-page-intro {
  margin-top: 1rem;
  color: var(--muted);
  font-size: 1.05rem;
  line-height: 1.7;
}

.keyword-cloud {
  position: relative;
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: center;
  gap: 1.05rem 1.2rem;
  min-height: 18rem;
  padding: 2rem 1.6rem 2.2rem;
  border: 1px solid var(--border);
  border-radius: calc(var(--radius) + 4px);
  background:
    radial-gradient(circle at 18% 22%, rgba(47, 111, 78, 0.08), transparent 42%),
    radial-gradient(circle at 82% 18%, rgba(29, 79, 122, 0.07), transparent 40%),
    radial-gradient(circle at 70% 88%, rgba(143, 74, 56, 0.06), transparent 38%),
    linear-gradient(165deg, #fffcf7 0%, #f7f4ee 100%);
  box-shadow: var(--shadow);
  overflow: hidden;
}

.keyword-chip {
  display: inline-flex;
  align-items: baseline;
  gap: 0.3rem;
  padding: 0.5rem 0.95rem;
  border-radius: 999px;
  border: 1px solid var(--chip-border, var(--border));
  background: var(--chip-bg, var(--accent-soft));
  color: var(--chip-fg, var(--accent));
  text-decoration: none;
  font-size: 0.95rem;
  font-weight: 700;
  line-height: 1.2;
  letter-spacing: 0.01em;
  box-shadow: 0 6px 16px rgba(31, 41, 55, 0.05);
  transform: translate(var(--dx, 0), var(--dy, 0)) rotate(var(--rot, 0deg));
  transition: transform 0.18s ease, box-shadow 0.18s ease, filter 0.18s ease;
}

.keyword-chip:hover {
  transform: translate(var(--dx, 0), calc(var(--dy, 0) - 3px)) rotate(var(--rot, 0deg)) scale(1.04);
  box-shadow: 0 10px 22px rgba(31, 41, 55, 0.1);
  filter: saturate(1.08);
  z-index: 1;
}

.keyword-count {
  font-size: 0.78em;
  font-weight: 800;
  opacity: 0.72;
}

.keyword-empty {
  color: var(--muted);
}

.keyword-empty code {
  font-size: 0.92em;
}

.book-list {
  display: grid;
  gap: 1rem;
}

.book-card {
  padding: 1.25rem 1.35rem;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--panel);
  box-shadow: var(--shadow);
}

.book-card-meta,
.book-article-meta {
  color: var(--muted);
  font-size: 0.92rem;
}

.book-card h2 {
  margin: 0.5rem 0 0.6rem;
  font-size: 1.35rem;
}

.book-card h2 a {
  text-decoration: none;
}

.book-card h2 a:hover {
  color: var(--accent);
}

.book-card p {
  margin: 0;
  color: var(--muted);
  line-height: 1.7;
}

.book-article {
  position: relative;
  display: grid;
  gap: 1.5rem;
}

.book-article-body {
  font-size: 1.02rem;
  line-height: 1.9;
}

.book-article-body h2,
.book-article-body h3 {
  margin-top: 2rem;
  margin-bottom: 0.8rem;
}

.book-article-body p,
.book-article-body ul,
.book-article-body ol,
.book-article-body pre,
.book-article-body blockquote {
  margin: 0 0 1rem;
}

.book-article-body ul,
.book-article-body ol {
  padding-left: 1.4rem;
}

.book-article-body a {
  color: var(--accent);
  text-decoration: none;
}

.book-article-body a:hover {
  text-decoration: underline;
}

.book-article-body code {
  padding: 0.16rem 0.4rem;
  border-radius: 8px;
  background: #eef3ee;
  font-size: 0.92em;
}

.book-article-body pre {
  overflow: auto;
  padding: 1rem 1.1rem;
  border-radius: 14px;
  background: #101828;
  color: #f9fafb;
  box-shadow: var(--shadow);
}

.book-article-body pre code {
  padding: 0;
  background: transparent;
  color: inherit;
}

.book-article-body blockquote {
  padding: 0.2rem 1rem;
  border-left: 4px solid var(--accent);
  background: #f1f7f3;
  color: #344054;
}

.book-article-body img {
  max-width: 100%;
  height: auto;
  border-radius: 16px;
}

.book-dot {
  margin: 0 0.5rem;
}

.video-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 1.5rem 1.25rem;
}

.video-card {
  display: block;
  text-decoration: none;
  color: inherit;
  transition: transform 0.2s ease;
}

.video-card:hover {
  transform: translateY(-3px);
}

.video-cover {
  overflow: hidden;
  border-radius: var(--radius);
  border: 1px solid var(--border);
  background: var(--panel);
  aspect-ratio: 16 / 10;
  box-shadow: var(--shadow);
}

.video-cover img,
.video-cover-fallback {
  display: block;
  width: 100%;
  height: 100%;
  object-fit: cover;
}

.video-cover-fallback {
  background: linear-gradient(135deg, #e7f1ea, #d7e8dc 55%, #c5dccb);
}

.video-title {
  margin: 0.75rem 0 0;
  font-size: 1.05rem;
  font-weight: 700;
  line-height: 1.4;
}

.video-date {
  display: block;
  margin-top: 0.35rem;
  color: var(--muted);
  font-size: 0.85rem;
}

.video-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
  margin-top: 0.45rem;
}

.video-tag {
  color: var(--muted);
  font-size: 0.78rem;
  font-weight: 600;
  line-height: 1.2;
  padding: 0.18rem 0.45rem;
  border-radius: 8px;
  background: var(--accent-soft);
  color: var(--accent);
}

.video-card:hover .video-title {
  color: var(--accent);
}

.video-empty {
  grid-column: 1 / -1;
  color: var(--muted);
}

@media (max-width: 960px) {
  .book-shell {
    grid-template-columns: 1fr;
  }

  .book-sidebar {
    position: fixed;
    inset: 0 auto 0 0;
    width: min(86vw, 340px);
    transform: translateX(-100%);
    transition: transform 0.25s ease;
    z-index: 20;
    box-shadow: var(--shadow);
  }

  body.sidebar-open .book-sidebar {
    transform: translateX(0);
  }

  .book-topbar {
    display: flex;
  }

  .book-content {
    padding: 1.5rem 1.1rem 3rem;
  }

  .video-grid {
    grid-template-columns: 1fr;
  }
}