:root {
  --navy: #01002a;
  --navy-light: #0a0838;
  --navy-lighter: #15134a;
  --cyan: #1affff;
  --cyan-dim: #0ccccc;
  --cyan-glow: rgba(26, 255, 255, .15);
  --ink: #e8e6f0;
  --ink-dim: #9895b0;
  --ink-muted: #6b6890;
  --card-bg: #0a0838;
  --border: rgba(26, 255, 255, .12);
  --border-light: rgba(26, 255, 255, .25);
  --maxw: 740px;
  --sidebar-w: 290px;
  --font: "Inter", -apple-system, "Segoe UI", system-ui, Roboto, Helvetica, Arial, sans-serif;
  --mono: "JetBrains Mono", "SF Mono", Consolas, monospace;
  --radius: 8px;
  --radius-sm: 6px;
  --transition: .2s ease;
}

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

body {
  background: var(--navy);
  color: var(--ink);
  font-family: var(--font);
  font-size: 17px;
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

::selection { background: var(--cyan); color: var(--navy); }

a { color: var(--cyan); text-decoration: none; transition: color var(--transition); }
a:hover { color: #fff; }

/* ─── Top bar ─── */
.topbar {
  height: 60px;
  display: flex;
  align-items: center;
  gap: 16px;
  padding: 0 24px;
  border-bottom: 1px solid var(--border);
  background: var(--navy);
  position: sticky;
  top: 0;
  z-index: 100;
}

.sidebar-toggle {
  display: none;
  background: none;
  border: 1px solid var(--border);
  color: var(--ink);
  font-size: 1.2rem;
  padding: 6px 10px;
  border-radius: var(--radius-sm);
  cursor: pointer;
  line-height: 1;
}

.brand {
  font-weight: 700;
  color: var(--cyan);
  font-size: 1.05rem;
  letter-spacing: -.03em;
  white-space: nowrap;
}
.brand:hover { color: var(--cyan); text-decoration: none; }

.search-box {
  flex: 1;
  max-width: 480px;
  margin-left: auto;
}
.search-box input {
  width: 100%;
  padding: 8px 14px;
  border: 1px solid var(--border);
  border-radius: 100px;
  background: var(--navy-light);
  color: var(--ink);
  font-family: var(--font);
  font-size: .88rem;
  outline: none;
  transition: border-color var(--transition), box-shadow var(--transition);
}
.search-box input::placeholder { color: var(--ink-muted); }
.search-box input:focus {
  border-color: var(--cyan);
  box-shadow: 0 0 0 3px var(--cyan-glow);
}

/* ─── Layout ─── */
.layout { display: flex; min-height: calc(100vh - 60px); }

.sidebar {
  width: var(--sidebar-w);
  flex: 0 0 var(--sidebar-w);
  border-right: 1px solid var(--border);
  background: var(--navy);
  padding: 20px 0 24px 0;
  position: sticky;
  top: 60px;
  height: calc(100vh - 60px);
  overflow-y: auto;
  overflow-x: hidden;
}

.sidebar::-webkit-scrollbar { width: 4px; }
.sidebar::-webkit-scrollbar-thumb { background: var(--border); border-radius: 10px; }
.sidebar::-webkit-scrollbar-track { background: transparent; }

.content {
  flex: 1;
  min-width: 0;
  padding: 48px 48px 64px;
  max-width: 960px;
}

/* ─── Search results in sidebar ─── */
.search-results {
  padding: 0 16px 12px;
  border-bottom: 1px solid var(--border);
  margin-bottom: 8px;
}
.search-results .result-item {
  display: block;
  padding: 8px 10px;
  border-radius: var(--radius-sm);
  color: var(--ink-dim);
  font-size: .88rem;
  transition: background var(--transition);
}
.search-results .result-item:hover {
  background: var(--navy-lighter);
  color: var(--ink);
  text-decoration: none;
}
.search-results .result-item em { color: var(--cyan); font-style: normal; font-weight: 600; }
.search-results .result-title { display: block; font-weight: 500; }
.search-results .result-snippet { display: block; font-size: .78rem; color: var(--ink-muted); margin-top: 2px; line-height: 1.4; }
.search-results .result-empty {
  color: var(--ink-muted);
  font-size: .85rem;
  padding: 8px 10px;
}

/* ─── Sidebar navigation ─── */
.sidebar-navigation { font-size: .92rem; }
.sidebar-navigation ul { list-style: none; margin: 0; padding: 0; }

.nav-section > ul.nav-children {
  max-height: 0;
  overflow: hidden;
  transition: max-height .3s ease, opacity .25s ease;
  opacity: 0;
}
.nav-section.expanded > ul.nav-children {
  max-height: 2000px;
  opacity: 1;
}

.nav-item {
  display: flex;
  align-items: center;
  padding: 1px 16px 1px 0;
}
.nav-item a {
  flex: 1;
  padding: 7px 12px 7px 16px;
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  color: var(--ink-dim);
  font-weight: 450;
  transition: background var(--transition), color var(--transition);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}
.nav-item a:hover { background: var(--navy-lighter); color: var(--ink); text-decoration: none; }
.nav-item a.active { color: var(--cyan); font-weight: 600; background: var(--cyan-glow); }
.nav-item a.folder-title { font-weight: 500; color: var(--ink); }
.nav-item a.folder-title.active { color: var(--cyan); }

.nav-chevron {
  flex: 0 0 22px;
  width: 22px;
  height: 22px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: none;
  border: 1px solid var(--border);
  border-radius: 4px;
  color: var(--ink-muted);
  font-size: .8rem;
  cursor: pointer;
  padding: 0;
  line-height: 1;
  transition: transform var(--transition), color var(--transition), border-color var(--transition);
}
.nav-chevron:hover { color: var(--cyan); border-color: var(--cyan); }
.nav-section.expanded > .nav-item .nav-chevron { transform: rotate(90deg); }

/* Nesting indent */
.nav-section > ul.nav-children .nav-item a { padding-left: 32px; }
.nav-section > ul.nav-children .nav-section > ul.nav-children .nav-item a { padding-left: 48px; }
.nav-section > ul.nav-children .nav-section > ul.nav-children .nav-section > ul.nav-children .nav-item a { padding-left: 64px; }

/* ─── Prose / article readability ─── */
article.prose {
  max-width: var(--maxw);
  margin: 0 auto;
}

article.prose h1 {
  font-size: 2.2rem;
  line-height: 1.25;
  margin: 0 0 .5em;
  font-weight: 700;
  letter-spacing: -.03em;
  color: #fff;
}
article.prose h2 {
  font-size: 1.5rem;
  margin: 2em 0 .4em;
  font-weight: 600;
  color: #fff;
  letter-spacing: -.02em;
  padding-bottom: .3em;
  border-bottom: 1px solid var(--border);
}
article.prose h3 {
  font-size: 1.2rem;
  margin: 1.6em 0 .3em;
  font-weight: 600;
  color: var(--ink);
}
article.prose p { margin: 0 0 1.2em; }
article.prose ul, article.prose ol { margin: 0 0 1.2em; padding-left: 1.5em; }
article.prose li { margin: .35em 0; }
article.prose a { text-decoration: underline; text-underline-offset: 2px; }
article.prose a:hover { color: var(--cyan); }
article.prose blockquote {
  border-left: 3px solid var(--cyan);
  margin: 1.6em 0;
  padding: .3em 0 .3em 1.2em;
  color: var(--ink-dim);
  font-style: italic;
  background: var(--navy-light);
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
}
article.prose code {
  font-family: var(--mono);
  font-size: .85em;
  background: var(--navy-lighter);
  padding: 2px 7px;
  border-radius: 4px;
  color: var(--cyan);
}
article.prose pre {
  background: var(--navy-light);
  border: 1px solid var(--border);
  padding: 18px 20px;
  border-radius: var(--radius);
  overflow-x: auto;
  margin: 0 0 1.4em;
  font-size: .9rem;
}
article.prose pre code { background: none; padding: 0; color: inherit; }
article.prose table {
  border-collapse: collapse;
  width: 100%;
  margin: 0 0 1.4em;
  font-size: .92rem;
  border-radius: var(--radius);
  overflow: hidden;
}
article.prose th, article.prose td {
  border: 1px solid var(--border);
  padding: 10px 14px;
  text-align: left;
}
article.prose th {
  background: var(--navy-lighter);
  font-weight: 600;
  color: #fff;
}
article.prose img { max-width: 100%; border-radius: var(--radius); }
article.prose hr { border: none; border-top: 1px solid var(--border); margin: 2.4em 0; }
article.prose strong { color: #fff; font-weight: 600; }
article.prose .katex-display {
  margin: 1.5em 0;
  overflow-x: auto;
  overflow-y: hidden;
  padding: .2rem 0;
}
article.prose .katex {
  color: #fff;
  font-size: 1.03em;
}
article.prose .katex-display > .katex {
  display: inline-block;
  max-width: 100%;
}
article.prose .math-fallback {
  display: inline-block;
  max-width: 100%;
  white-space: pre-wrap;
}

/* ─── Article tools (bookmark, rating, share) ─── */
.article-tools {
  margin-top: 56px;
  padding-top: 28px;
  border-top: 1px solid var(--border);
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 20px;
}

.bookmark-btn {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: none;
  border: 1px solid var(--border);
  color: var(--ink-dim);
  padding: 8px 16px;
  border-radius: var(--radius-sm);
  cursor: pointer;
  font-family: var(--font);
  font-size: .88rem;
  transition: background var(--transition), border-color var(--transition), color var(--transition);
}
.bookmark-btn:hover { border-color: var(--cyan); color: var(--cyan); }
.bookmark-btn.bookmarked { border-color: var(--cyan); color: var(--cyan); background: var(--cyan-glow); }

.rating-stars {
  display: inline-flex;
  gap: 2px;
}
.rating-stars .star {
  font-size: 1.4rem;
  color: var(--ink-muted);
  cursor: pointer;
  transition: color var(--transition), transform var(--transition);
  user-select: none;
}
.rating-stars .star:hover,
.rating-stars .star.active { color: #ffd200; }
.rating-stars .star:hover { transform: scale(1.2); }

.li-share {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: var(--cyan);
  color: var(--navy);
  font-weight: 600;
  padding: 8px 18px;
  border-radius: 100px;
  font-size: .88rem;
  transition: background var(--transition), transform var(--transition);
  margin-left: auto;
}
.li-share:hover {
  background: #fff;
  color: var(--navy);
  text-decoration: none;
  transform: translateY(-1px);
}

/* ─── Home page ─── */
.home-hero {
  text-align: center;
  padding: 48px 0 24px;
}
.home-hero h1 {
  font-size: 2.6rem;
  font-weight: 700;
  margin: 0 0 .3em;
  letter-spacing: -.03em;
  color: #fff;
}
.home-hero p.lead {
  font-size: 1.1rem;
  color: var(--ink-dim);
  max-width: 600px;
  margin: 0 auto 40px;
}
.home-index {
  list-style: none;
  padding: 0;
  max-width: 500px;
  margin: 0 auto;
}
.home-index li { margin: 6px 0; }
.home-index a {
  display: block;
  padding: 14px 20px;
  background: var(--navy-light);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  font-weight: 500;
  color: var(--ink);
  transition: background var(--transition), border-color var(--transition), transform var(--transition);
}
.home-index a:hover {
  border-color: var(--cyan);
  background: var(--navy-lighter);
  color: var(--cyan);
  text-decoration: none;
  transform: translateX(4px);
}

/* ─── Footer ─── */
.sitefoot {
  padding: 20px 32px;
  color: var(--ink-muted);
  font-size: .82rem;
  border-top: 1px solid var(--border);
  text-align: center;
}

/* ─── 404 ─── */
.not-found {
  text-align: center;
  padding: 80px 0;
}
.not-found h1 { font-size: 4rem; color: var(--cyan); margin: 0 0 .3em; }
.not-found p { color: var(--ink-dim); font-size: 1.05rem; }

/* ─── Responsive ─── */
@media (max-width: 900px) {
  .sidebar-toggle { display: block; }
  .sidebar {
    position: fixed;
    top: 60px;
    left: -100%;
    height: calc(100vh - 60px);
    z-index: 90;
    transition: left .3s ease;
    box-shadow: 4px 0 20px rgba(0,0,0,.4);
  }
  .sidebar.open { left: 0; }
  .content { padding: 32px 24px 40px; }
  .search-box { max-width: none; }
  .article-tools { flex-direction: column; align-items: flex-start; }
  .li-share { margin-left: 0; }
}

@media (max-width: 600px) {
  body { font-size: 16px; }
  .topbar { padding: 0 12px; gap: 10px; }
  .content { padding: 24px 16px 32px; }
  article.prose h1 { font-size: 1.7rem; }
  article.prose h2 { font-size: 1.25rem; }
  .home-hero h1 { font-size: 1.8rem; }
  .brand { font-size: .9rem; }
}