:root {
  --font-sans: "IBM Plex Sans", "Segoe UI", sans-serif;
  --font-mono: "IBM Plex Mono", ui-monospace, Menlo, Consolas, monospace;
  --radius: 14px;
  --accent: #14b8a6;
  --accent-strong: #0d9488;
  --shadow: 0 12px 40px rgba(15, 23, 42, 0.08);
  color-scheme: light;
}

html[data-theme="light"] {
  --bg: #f1f5f9;
  --bg-elevated: #ffffff;
  --text: #0f172a;
  --muted: #64748b;
  --border: #e2e8f0;
  --code-bg: #0f172a;
  --code-text: #e2e8f0;
  --nav-bg: rgba(255, 255, 255, 0.86);
  --hero-glow: rgba(20, 184, 166, 0.18);
  color-scheme: light;
}

html[data-theme="dark"] {
  --bg: #0f172a;
  --bg-elevated: #1e293b;
  --text: #f1f5f9;
  --muted: #94a3b8;
  --border: #334155;
  --code-bg: #020617;
  --code-text: #e2e8f0;
  --nav-bg: rgba(15, 23, 42, 0.9);
  --hero-glow: rgba(20, 184, 166, 0.22);
  --shadow: 0 12px 40px rgba(0, 0, 0, 0.35);
  color-scheme: dark;
}

*,
*::before,
*::after {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  min-height: 100vh;
  font-family: var(--font-sans);
  background:
    radial-gradient(900px 420px at 12% -10%, var(--hero-glow), transparent 60%),
    radial-gradient(700px 380px at 90% 0%, rgba(148, 163, 184, 0.12), transparent 55%),
    var(--bg);
  color: var(--text);
  line-height: 1.6;
}

a {
  color: var(--accent-strong);
  text-decoration-thickness: 1px;
  text-underline-offset: 0.18em;
}

a:hover {
  color: var(--accent);
}

.shell {
  width: min(1080px, calc(100% - 2rem));
  margin: 0 auto;
}

.topbar {
  position: sticky;
  top: 0;
  z-index: 20;
  backdrop-filter: blur(14px);
  background: var(--nav-bg);
  border-bottom: 1px solid var(--border);
}

.topbar-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: 0.85rem 0;
  flex-wrap: wrap;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 0.75rem;
  color: inherit;
  text-decoration: none;
}

.brand img {
  width: 42px;
  height: 42px;
  border-radius: 10px;
}

.brand-text {
  font-family: var(--font-mono);
  font-weight: 700;
  letter-spacing: -0.04em;
  font-size: 1.25rem;
}

.brand-text span {
  color: var(--muted);
  font-weight: 500;
  font-size: 0.72rem;
  display: block;
  letter-spacing: 0;
  margin-top: 0.05rem;
}

.nav {
  display: flex;
  flex-wrap: wrap;
  gap: 0.35rem 0.85rem;
  align-items: center;
}

.nav a {
  color: var(--muted);
  text-decoration: none;
  font-size: 0.92rem;
  padding: 0.25rem 0;
  border-bottom: 2px solid transparent;
}

.nav a:hover,
.nav a[aria-current="page"] {
  color: var(--text);
  border-bottom-color: var(--accent);
}

.controls {
  display: flex;
  gap: 0.5rem;
  align-items: center;
}

.controls select,
.controls button {
  font: inherit;
  font-family: var(--font-mono);
  font-size: 0.78rem;
  border: 1px solid var(--border);
  background: var(--bg-elevated);
  color: var(--text);
  border-radius: 999px;
  padding: 0.4rem 0.75rem;
  cursor: pointer;
}

.controls button:hover,
.controls select:hover {
  border-color: var(--accent);
}

main {
  padding: 2.25rem 0 4rem;
}

.hero {
  display: grid;
  gap: 1.25rem;
  padding: 1.5rem 0 2rem;
}

.hero img.lockup {
  width: min(360px, 100%);
  height: auto;
}

html[data-theme="dark"] .hero img.lockup {
  filter: invert(1) hue-rotate(180deg) brightness(1.05) contrast(1.05);
  /* lockup is dark-on-light; invert carefully — better use CSS filter sparingly */
  filter: none;
}

.hero h1 {
  margin: 0;
  font-family: var(--font-mono);
  font-size: clamp(1.8rem, 4vw, 2.6rem);
  letter-spacing: -0.04em;
  line-height: 1.15;
}

.hero .lede {
  margin: 0;
  max-width: 42rem;
  color: var(--muted);
  font-size: 1.05rem;
}

.pill-row {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.pill {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  border: 1px solid var(--border);
  background: var(--bg-elevated);
  border-radius: 999px;
  padding: 0.35rem 0.7rem;
  color: var(--muted);
}

.pill strong {
  color: var(--accent-strong);
  font-weight: 600;
}

.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 1rem;
  margin: 1.5rem 0;
}

.card {
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.1rem 1.15rem;
  box-shadow: var(--shadow);
}

.card h3 {
  margin: 0 0 0.4rem;
  font-family: var(--font-mono);
  font-size: 0.95rem;
  letter-spacing: -0.03em;
}

.card p {
  margin: 0;
  color: var(--muted);
  font-size: 0.92rem;
}

.card a {
  text-decoration: none;
}

.author-block {
  margin-top: 2.5rem;
  padding-top: 1.25rem;
  border-top: 1px solid var(--border);
}

.author-block p {
  margin: 0.15rem 0;
}

.mermaid-wrap {
  margin: 1.5rem 0;
  padding: 1.1rem 1rem;
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  overflow-x: auto;
}

.mermaid-wrap .mermaid,
.mermaid-wrap pre.mermaid,
.content .mermaid-wrap .mermaid,
.content .mermaid-wrap pre.mermaid {
  margin: 0;
  padding: 0.35rem 0;
  background: transparent !important;
  border: none !important;
  color: var(--text);
  text-align: center;
  overflow: visible;
  font-family: var(--font-sans);
  font-size: 0.9rem;
  line-height: 1.4;
  white-space: normal;
}

.mermaid-wrap .mermaid-pending {
  color: var(--muted);
  font-family: var(--font-mono);
  font-size: 0.8rem;
  white-space: pre-wrap;
  text-align: left;
}

.mermaid-wrap .mermaid-error {
  color: var(--muted);
  font-family: var(--font-mono);
  font-size: 0.8rem;
  white-space: pre-wrap;
  text-align: left;
}

.mermaid-wrap svg {
  max-width: 100%;
  height: auto;
  display: block;
  margin: 0 auto;
}

.content h1,
.content h2,
.content h3 {
  font-family: var(--font-mono);
  letter-spacing: -0.03em;
  line-height: 1.25;
}

.content h1 {
  font-size: 1.9rem;
  margin: 0 0 1rem;
}

.content h2 {
  font-size: 1.25rem;
  margin: 2rem 0 0.75rem;
  padding-bottom: 0.35rem;
  border-bottom: 1px solid var(--border);
  scroll-margin-top: 5rem;
}

.course-toc {
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1rem 1.25rem 1.15rem;
  margin: 1.25rem 0 1.75rem;
  box-shadow: var(--shadow);
}

.course-toc h2 {
  margin: 0 0 0.65rem;
  border: none;
  padding: 0;
  font-size: 1rem;
}

.course-toc ol {
  margin: 0;
  padding-left: 1.25rem;
}

.course-toc li {
  margin: 0.25rem 0;
}

.course-toc a {
  text-decoration: none;
}

.course-toc a:hover {
  text-decoration: underline;
}

.callout {
  border-left: 3px solid var(--accent);
  background: color-mix(in srgb, var(--accent) 10%, var(--bg-elevated));
  padding: 0.85rem 1rem;
  border-radius: 0 10px 10px 0;
  margin: 1.1rem 0;
}

.content h3 {
  font-size: 1.05rem;
  margin: 1.4rem 0 0.5rem;
}

.content p,
.content li {
  color: var(--text);
}

.content .muted,
.content p.muted {
  color: var(--muted);
}

.content pre {
  background: var(--code-bg);
  color: var(--code-text);
  border-radius: 12px;
  padding: 1rem 1.1rem;
  overflow-x: auto;
  border: 1px solid var(--border);
  font-family: var(--font-mono);
  font-size: 0.84rem;
  line-height: 1.5;
}

.content code {
  font-family: var(--font-mono);
  font-size: 0.9em;
}

.content :not(pre) > code {
  background: color-mix(in srgb, var(--accent) 12%, var(--bg-elevated));
  color: var(--text);
  padding: 0.1em 0.35em;
  border-radius: 6px;
}

.content table {
  width: 100%;
  border-collapse: collapse;
  margin: 1rem 0;
  font-size: 0.92rem;
}

.content th,
.content td {
  border: 1px solid var(--border);
  padding: 0.55rem 0.7rem;
  text-align: left;
  vertical-align: top;
}

.content th {
  background: var(--bg-elevated);
  font-family: var(--font-mono);
  font-size: 0.82rem;
}

.content ul {
  padding-left: 1.2rem;
}

.footer {
  border-top: 1px solid var(--border);
  padding: 1.5rem 0 2.5rem;
  color: var(--muted);
  font-size: 0.88rem;
}

.footer a {
  color: var(--muted);
}

@media (max-width: 720px) {
  .topbar-inner {
    align-items: flex-start;
  }
  .nav {
    width: 100%;
    order: 3;
  }
}