:root {
  --primary-blue: #0F4C81;
  --deep-purple: #3A1078;
  --vibrant-teal: #00A8CC;
  --concept-orange: #FF6B6B;
  --concept-yellow: #FFA834;
  --example-green: #2ECC71;
  --code-bg: #F8F9FA;
  --dark-charcoal: #2D3748;
  --sidebar-width: 300px;
  --page-bg: #FAFBFC;
  --border-soft: #E5E9F0;
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  background: var(--page-bg);
  color: var(--dark-charcoal);
  font-family: "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  line-height: 1.65;
  font-size: 16px;
  -webkit-font-smoothing: antialiased;
}

.layout {
  display: flex;
  min-height: 100vh;
}

/* ---------------- Sidebar ---------------- */

.sidebar {
  width: var(--sidebar-width);
  flex-shrink: 0;
  background: linear-gradient(180deg, var(--deep-purple) 0%, #2a0c5c 100%);
  color: #fff;
  position: sticky;
  top: 0;
  height: 100vh;
  display: flex;
  flex-direction: column;
  z-index: 50;
}

.sidebar-header {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 18px 18px 14px 18px;
  border-bottom: 1px solid rgba(255,255,255,0.12);
}

.brand-logo {
  height: 34px;
  width: auto;
  border-radius: 6px;
}

.brand-text {
  font-weight: 700;
  font-size: 15px;
  line-height: 1.2;
  letter-spacing: 0.2px;
}

.brand-text span {
  display: block;
  font-weight: 400;
  font-size: 11px;
  opacity: 0.65;
  margin-top: 2px;
}

.sidebar-scroll {
  overflow-y: auto;
  padding: 10px 0 30px 0;
  flex: 1;
}

.sidebar-scroll::-webkit-scrollbar { width: 7px; }
.sidebar-scroll::-webkit-scrollbar-thumb { background: rgba(255,255,255,0.18); border-radius: 4px; }

.toc-root { list-style: none; margin: 0; padding: 0 10px; }
.toc-root ul { list-style: none; margin: 0; padding-left: 14px; }

.toc-chapter { margin-bottom: 2px; }

.toc-chapter > details > summary {
  cursor: pointer;
  list-style: none;
  padding: 4px 8px;
  border-radius: 8px;
}
.toc-chapter > details > summary::-webkit-details-marker { display: none; }
.toc-chapter > details > summary::before {
  content: "\25B8";
  display: inline-block;
  margin-right: 6px;
  font-size: 11px;
  opacity: 0.6;
  transition: transform 0.15s ease;
}
.toc-chapter > details[open] > summary::before { transform: rotate(90deg); }

.toc-chapter > details > summary:hover { background: rgba(255,255,255,0.08); }

.chapter-link {
  color: #fff;
  text-decoration: none;
  font-weight: 600;
  font-size: 13.5px;
}
.chapter-link.active { color: var(--concept-yellow); }

.toc-sections { padding-top: 2px; padding-bottom: 6px; }

.toc-l1 > a { font-weight: 600; font-size: 13px; }
.toc-l2 > a { font-weight: 400; font-size: 12.3px; opacity: 0.88; }
.toc-l3 > a { font-weight: 400; font-size: 11.8px; opacity: 0.72; }

.toc-link {
  display: block;
  color: #E4E1F5;
  text-decoration: none;
  padding: 4px 8px;
  border-radius: 6px;
  border-left: 2px solid transparent;
  margin: 1px 0;
}
.toc-link:hover { background: rgba(255,255,255,0.1); color: #fff; }
.toc-link.current {
  background: rgba(255,168,52,0.18);
  border-left-color: var(--concept-yellow);
  color: #fff;
}

/* ---------------- Main content ---------------- */

.content {
  flex: 1;
  min-width: 0;
}

.content-inner {
  max-width: 880px;
  margin: 0 auto;
  padding: 48px 40px 80px 40px;
}

.chapter-eyebrow {
  text-transform: uppercase;
  letter-spacing: 1.5px;
  font-size: 12.5px;
  font-weight: 700;
  color: var(--vibrant-teal);
  margin-bottom: 6px;
}

.chapter-header h1 {
  font-size: 34px;
  margin: 0 0 8px 0;
  color: var(--deep-purple);
  font-weight: 800;
  letter-spacing: -0.3px;
}

.chapter-header {
  padding-bottom: 22px;
  margin-bottom: 30px;
  border-bottom: 3px solid var(--border-soft);
}

.content-section { scroll-margin-top: 20px; }

.section-heading {
  color: var(--primary-blue);
  font-weight: 800;
}

h2.section-heading {
  font-size: 25px;
  margin-top: 46px;
  padding-top: 6px;
  border-top: 1px solid var(--border-soft);
}
.content-section.level-1:first-of-type h2.section-heading,
.chapter-header + .content-section h2.section-heading {
  border-top: none;
  margin-top: 8px;
}

h3.section-heading {
  font-size: 20px;
  margin-top: 34px;
  color: var(--deep-purple);
}

h4.section-heading {
  font-size: 16.5px;
  margin-top: 26px;
  color: var(--dark-charcoal);
  text-transform: uppercase;
  letter-spacing: 0.4px;
  font-weight: 700;
  opacity: 0.85;
}

p { margin: 12px 0; }

ul, ol {
  margin: 10px 0;
  padding-left: 26px;
}
li { margin: 4px 0; }

code {
  background: #EFF1F5;
  padding: 1px 5px;
  border-radius: 4px;
  font-family: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
  font-size: 0.92em;
  color: #B4231E;
}

/* ---------------- Boxes ---------------- */

.concept-box, .concept-box-alt, .example-box {
  border-radius: 10px;
  margin: 20px 0;
  overflow: hidden;
  box-shadow: 0 1px 3px rgba(0,0,0,0.06);
}

.concept-box {
  border: 1.5px solid var(--concept-orange);
  background: #fff;
}
.concept-box .box-title {
  background: linear-gradient(90deg, var(--concept-orange), var(--concept-yellow));
  color: #fff;
  font-weight: 700;
  padding: 9px 16px;
  font-size: 15px;
}
.concept-box .box-body { padding: 14px 18px 16px 18px; }

.concept-box-alt {
  border: 1.5px solid #7E57C2;
  background: #fff;
}
.concept-box-alt .box-title {
  background: linear-gradient(90deg, #7E57C2, var(--vibrant-teal));
  color: #fff;
  font-weight: 700;
  padding: 9px 16px;
  font-size: 15px;
}
.concept-box-alt .box-body { padding: 14px 18px 16px 18px; }

.example-box {
  border: 1px solid var(--example-green);
  border-left: 4px solid var(--example-green);
  background: #F4FCF7;
}
.example-box .box-title {
  color: #1c8a4c;
  font-weight: 700;
  padding: 10px 16px 0 16px;
  font-size: 14.5px;
}
.example-box .box-body { padding: 6px 18px 14px 18px; }
.example-box .box-body p:first-child { margin-top: 4px; }

/* ---------------- Code blocks ---------------- */

.code-box {
  margin: 20px 0;
  border-radius: 10px;
  overflow: hidden;
  border: 1px solid var(--vibrant-teal);
}
.code-title {
  background: var(--vibrant-teal);
  color: #fff;
  font-weight: 700;
  font-family: "SFMono-Regular", Consolas, monospace;
  font-size: 13px;
  padding: 8px 16px;
}
.code-box pre {
  background: var(--code-bg);
  margin: 0;
  padding: 14px 18px;
  overflow-x: auto;
}
.code-box code {
  background: none;
  color: var(--dark-charcoal);
  padding: 0;
  font-size: 13.5px;
  line-height: 1.55;
}

/* ---------------- Figures ---------------- */

.figure-wrap {
  margin: 22px 0;
  text-align: center;
}
.figure-wrap img {
  max-width: 100%;
  height: auto;
}

/* ---------------- Pager / footer ---------------- */

.chapter-pager {
  display: flex;
  margin-top: 60px;
  padding-top: 24px;
  border-top: 1px solid var(--border-soft);
  gap: 12px;
}
.spacer { flex: 1; }
.nav-btn {
  color: var(--primary-blue);
  text-decoration: none;
  font-weight: 600;
  font-size: 14px;
  padding: 10px 16px;
  border: 1.5px solid var(--border-soft);
  border-radius: 8px;
  max-width: 46%;
}
.nav-btn:hover { border-color: var(--primary-blue); background: #F0F5FA; }

.page-footer {
  margin-top: 50px;
  padding-top: 18px;
  border-top: 1px solid var(--border-soft);
  font-size: 12.5px;
  color: #94A0B4;
  text-align: center;
}

/* ---------------- Landing page ---------------- */

.chapter-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: 18px;
  margin-top: 20px;
}

.chapter-card {
  display: block;
  text-decoration: none;
  color: inherit;
  border: 1.5px solid var(--border-soft);
  border-radius: 12px;
  padding: 18px 20px;
  background: #fff;
  transition: border-color 0.15s ease, transform 0.15s ease, box-shadow 0.15s ease;
}
.chapter-card:hover {
  border-color: var(--vibrant-teal);
  transform: translateY(-2px);
  box-shadow: 0 8px 20px rgba(15,76,129,0.1);
}
.chapter-card-num {
  font-size: 11.5px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 1px;
  color: var(--vibrant-teal);
  margin-bottom: 6px;
}
.chapter-card-title {
  font-size: 19px;
  font-weight: 800;
  color: var(--deep-purple);
  margin-bottom: 6px;
}
.chapter-card-meta {
  font-size: 12.5px;
  color: #94A0B4;
  margin-bottom: 10px;
}
.chapter-card-preview {
  font-size: 13px;
  color: #5B6472;
  line-height: 1.5;
}

/* ---------------- Static / policy pages ---------------- */

.static-page .content-inner { max-width: 760px; }
.static-page h2 { color: var(--deep-purple); margin-top: 34px; font-size: 21px; }
.static-page h3 { color: var(--primary-blue); margin-top: 24px; font-size: 17px; }
.static-page ul { margin: 10px 0; }
.static-page .updated-date { color: #94A0B4; font-size: 13px; margin-top: -6px; }
.site-footer-links {
  margin-top: 60px;
  padding-top: 22px;
  border-top: 1px solid var(--border-soft);
  display: flex;
  flex-wrap: wrap;
  gap: 8px 22px;
  font-size: 13px;
  justify-content: center;
}
.site-footer-links a {
  color: #64748B;
  text-decoration: none;
}
.site-footer-links a:hover { color: var(--primary-blue); text-decoration: underline; }
.site-footer-copy {
  text-align: center;
  font-size: 12px;
  color: #B0B8C4;
  margin-top: 10px;
}

/* ---------------- Mobile ---------------- */

.menu-toggle {
  display: none;
  position: fixed;
  top: 12px;
  left: 12px;
  z-index: 100;
  background: var(--deep-purple);
  color: #fff;
  border: none;
  width: 40px;
  height: 40px;
  border-radius: 8px;
  font-size: 18px;
  cursor: pointer;
}
.sidebar-overlay { display: none; }

@media (max-width: 920px) {
  .menu-toggle { display: block; }
  .sidebar {
    position: fixed;
    left: 0; top: 0;
    transform: translateX(-100%);
    transition: transform 0.2s ease;
    box-shadow: 4px 0 20px rgba(0,0,0,0.2);
  }
  .sidebar.open { transform: translateX(0); }
  .sidebar-overlay {
    display: none;
    position: fixed;
    inset: 0;
    background: rgba(0,0,0,0.35);
    z-index: 40;
  }
  .sidebar-overlay.show { display: block; }
  .content-inner { padding: 70px 20px 60px 20px; }
  .chapter-header h1 { font-size: 26px; }
  .nav-btn { max-width: 100%; font-size: 13px; }
}