@import url('https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700&family=JetBrains+Mono:wght@400;500&display=swap');

/* ---------- design tokens (light) ---------- */
:root {
  --color-background-tertiary: #f8fafc;   /* page bg */
  --color-background-primary: #ffffff;     /* cards/surfaces */
  --color-background-secondary: #f1f5f9;   /* soft fills */
  --color-background-info: #eef2ff;
  --color-background-success: #f0fdf4;
  --color-background-warning: #fffbeb;
  --color-background-danger: #fef2f2;

  --color-text-primary: #0f172a;
  --color-text-secondary: #475569;
  --color-text-tertiary: #94a3b8;
  --color-text-info: #4338ca;
  --color-text-success: #15803d;
  --color-text-warning: #b45309;
  --color-text-danger: #dc2626;

  --color-border-tertiary: #e2e8f0;
  --color-border-secondary: #cbd5e1;
  --color-border-danger: #dc2626;

  --accent: #4f46e5;
  --accent-text: #4338ca;
  --accent-contrast: #ffffff;

  --border-radius-md: 8px;
  --border-radius-lg: 14px;
  --border-radius-xl: 20px;
  --font-sans: "Inter", system-ui, -apple-system, sans-serif;
  --font-mono: "JetBrains Mono", ui-monospace, Menlo, monospace;
  --shadow: 0 1px 2px rgba(15,23,42,.04), 0 4px 16px rgba(15,23,42,.05);
  --maxw: 920px;
}

/* ---------- design tokens (dark) ---------- */
[data-theme="dark"] {
  --color-background-tertiary: #0b1120;
  --color-background-primary: #131a2a;
  --color-background-secondary: #1e293b;
  --color-background-info: #1e1b4b;
  --color-background-success: #052e16;
  --color-background-warning: #422006;
  --color-background-danger: #450a0a;

  --color-text-primary: #f1f5f9;
  --color-text-secondary: #94a3b8;
  --color-text-tertiary: #64748b;
  --color-text-info: #a5b4fc;
  --color-text-success: #4ade80;
  --color-text-warning: #fbbf24;
  --color-text-danger: #f87171;

  --color-border-tertiary: #1e293b;
  --color-border-secondary: #334155;
  --color-border-danger: #f87171;

  --accent: #818cf8;
  --accent-text: #a5b4fc;
  --accent-contrast: #0b1120;

  --shadow: 0 1px 2px rgba(0,0,0,.3), 0 6px 20px rgba(0,0,0,.4);
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  font-family: var(--font-sans);
  color: var(--color-text-primary);
  background: var(--color-background-tertiary);
  max-width: var(--maxw);
  margin: 0 auto;
  padding: 0 1.5rem 5rem;
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
  transition: background-color .2s ease, color .2s ease;
}

a { color: var(--accent-text); text-decoration: none; }
a:hover { text-decoration: underline; }

code {
  font-family: var(--font-mono);
  font-size: .88em;
  background: var(--color-background-secondary);
  color: var(--color-text-primary);
  padding: 2px 6px;
  border-radius: 6px;
}

/* ---------- top bar ---------- */
.topbar {
  position: sticky; top: 0; z-index: 10;
  display: flex; align-items: center; justify-content: space-between;
  gap: 1rem;
  padding: .85rem 0;
  margin-bottom: 1.5rem;
  background: color-mix(in srgb, var(--color-background-tertiary) 88%, transparent);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--color-border-tertiary);
}
.topbar .brand {
  font-weight: 600; font-size: 15px; color: var(--color-text-primary);
  display: inline-flex; align-items: center; gap: .5rem;
}
.topbar .brand .dot { width: 9px; height: 9px; border-radius: 50%; background: var(--accent); }
.theme-toggle {
  font-size: 16px; line-height: 1; width: 38px; height: 38px;
  border-radius: var(--border-radius-md);
  border: 1px solid var(--color-border-secondary);
  background: var(--color-background-primary);
  color: var(--color-text-primary); cursor: pointer;
  display: inline-flex; align-items: center; justify-content: center;
  transition: background-color .15s ease, border-color .15s ease;
}
.theme-toggle:hover { background: var(--color-background-secondary); }
.topnav { display: flex; gap: 1.35rem; align-items: center; }
.topnav a { font-size: 14px; color: var(--color-text-secondary); }
.topnav a:hover { color: var(--accent-text); text-decoration: none; }
@media (max-width: 640px) { .topnav { display: none; } }
.byline { margin: 1rem 0 0; font-size: 14px; color: var(--color-text-secondary); }
.byline a { color: var(--accent-text); }

/* ---------- hero ---------- */
.hero { padding: 2.5rem 0 1.5rem; }
.hero h1 {
  font-size: clamp(30px, 6vw, 44px); font-weight: 700; letter-spacing: -.02em;
  margin: 0 0 .5rem; line-height: 1.1;
}
.hero .tagline { font-size: clamp(16px, 2.5vw, 19px); color: var(--color-text-secondary); margin: 0; max-width: 640px; }
.badges { display: flex; gap: 8px; flex-wrap: wrap; margin-top: 1.5rem; }
.badge {
  font-family: var(--font-mono); font-size: 12px; font-weight: 500;
  background: var(--color-background-secondary); color: var(--color-text-secondary);
  padding: 5px 11px; border-radius: 999px; border: 1px solid var(--color-border-tertiary);
}
.badge.accent { background: var(--accent); color: var(--accent-contrast); border-color: transparent; }

/* ---------- headings / sections ---------- */
h1 { font-size: 26px; font-weight: 600; letter-spacing: -.01em; margin: 1.5rem 0 .5rem; }
h2 { font-size: 24px; font-weight: 600; letter-spacing: -.01em; margin: 3rem 0 .5rem; }
h3 { font-size: 16px; font-weight: 600; margin: 0 0 .35rem; }
p.lead { color: var(--color-text-secondary); margin: .25rem 0 1.25rem; }

/* ---------- cards ---------- */
.grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(250px, 1fr)); gap: 14px; margin: 1rem 0; }
.card {
  display: flex; flex-direction: column;
  background: var(--color-background-primary);
  border: 1px solid var(--color-border-tertiary);
  border-radius: var(--border-radius-lg);
  padding: 1.1rem 1.25rem; color: var(--color-text-primary);
  transition: transform .15s ease, border-color .15s ease, box-shadow .15s ease;
}
.card:hover { transform: translateY(-2px); border-color: var(--accent); box-shadow: var(--shadow); text-decoration: none; }
.card p { margin: 0; font-size: 14px; color: var(--color-text-secondary); }
.card .meta {
  margin-top: .75rem; font-family: var(--font-mono); font-size: 12px;
  color: var(--accent-text); font-weight: 500;
}

/* ---------- two-column lists ---------- */
.cols { display: grid; grid-template-columns: repeat(auto-fit, minmax(240px, 1fr)); gap: 1.5rem; margin: 1rem 0; }
.col h3 { font-size: 14px; text-transform: uppercase; letter-spacing: .05em; color: var(--color-text-tertiary); }
.col ul { margin: .25rem 0; padding-left: 1.1rem; }
.col li { font-size: 14px; color: var(--color-text-secondary); margin: .3rem 0; }

/* ---------- buttons (used by visualizations) ---------- */
button:not(.theme-toggle) {
  font-family: inherit; font-size: 14px; font-weight: 500;
  padding: 8px 15px; border-radius: var(--border-radius-md);
  border: 1px solid var(--color-border-secondary);
  background: var(--color-background-primary); color: var(--color-text-primary);
  cursor: pointer; transition: background-color .15s ease, border-color .15s ease, transform .1s ease;
}
button:not(.theme-toggle):hover { background: var(--color-background-secondary); border-color: var(--accent); }
button:not(.theme-toggle):active { transform: scale(.98); }
button:disabled { opacity: .4; cursor: default; }

/* ---------- footer ---------- */
footer {
  margin-top: 4rem; padding-top: 1.5rem;
  border-top: 1px solid var(--color-border-tertiary);
  color: var(--color-text-tertiary); font-size: 14px;
}

/* ---------- premium touches ---------- */
.accent-bar {
  position: fixed; top: 0; left: 0; right: 0; height: 3px; z-index: 50;
  background: linear-gradient(90deg, #6366f1, #a855f7, #ec4899);
}
.hero { position: relative; }
.hero .eyebrow {
  font-family: var(--font-mono); font-size: 13px; color: var(--accent-text);
  letter-spacing: .02em; margin: 0 0 .9rem;
}
.mono-line {
  display: inline-flex; align-items: center; gap: .55rem; margin-top: 1.5rem;
  font-family: var(--font-mono); font-size: 13px; color: var(--color-text-secondary);
  background: var(--color-background-secondary); border: 1px solid var(--color-border-tertiary);
  border-radius: 999px; padding: 7px 15px;
}
.mono-line .ok { color: var(--color-text-success); font-weight: 500; }

/* hero two-column + CTAs + code panel */
.hero-grid { display: grid; grid-template-columns: 1.05fr .95fr; gap: 2.5rem; align-items: center; }
@media (max-width: 780px) { .hero-grid { grid-template-columns: 1fr; gap: 1.75rem; } }
.cta-row { display: flex; gap: 10px; flex-wrap: wrap; margin-top: 1.6rem; }
.cta {
  display: inline-flex; align-items: center; gap: .4rem; font-size: 14px; font-weight: 500;
  padding: 10px 18px; border-radius: var(--border-radius-md); border: 1px solid var(--color-border-secondary);
  transition: filter .15s ease, background-color .15s ease, transform .1s ease;
}
.cta:hover { text-decoration: none; }
.cta:active { transform: scale(.98); }
.cta-primary { background: var(--accent); color: #fff; border-color: transparent; }
.cta-primary:hover { filter: brightness(1.08); }
.cta-secondary { background: var(--color-background-primary); color: var(--color-text-primary); }
.cta-secondary:hover { background: var(--color-background-secondary); }

.code-card {
  background: var(--color-background-primary); border: 1px solid var(--color-border-tertiary);
  border-radius: var(--border-radius-lg); overflow: hidden; box-shadow: var(--shadow);
}
.code-card .titlebar {
  display: flex; align-items: center; gap: 7px; padding: 10px 14px;
  border-bottom: 1px solid var(--color-border-tertiary); background: var(--color-background-secondary);
}
.code-card .titlebar .d { width: 11px; height: 11px; border-radius: 50%; }
.code-card .titlebar .fname { margin-left: 8px; font-family: var(--font-mono); font-size: 12px; color: var(--color-text-tertiary); }
.code-card pre { margin: 0; padding: 15px 16px; font-family: var(--font-mono); font-size: 12.5px; line-height: 1.75; overflow-x: auto; }
.tok-kw { color: #c026d3; } .tok-type { color: #0891b2; } .tok-fn { color: #2563eb; }
.tok-str { color: #16a34a; } .tok-num { color: #ea580c; } .tok-com { color: var(--color-text-tertiary); font-style: italic; }
[data-theme="dark"] .tok-kw { color: #e879f9; } [data-theme="dark"] .tok-type { color: #22d3ee; }
[data-theme="dark"] .tok-fn { color: #60a5fa; } [data-theme="dark"] .tok-str { color: #4ade80; } [data-theme="dark"] .tok-num { color: #fb923c; }

.kicker {
  font-family: var(--font-mono); font-size: 12px; letter-spacing: .1em;
  text-transform: uppercase; color: var(--accent-text); margin: 3.25rem 0 0;
}
.kicker + h2 { margin-top: .4rem; }

.card { position: relative; overflow: hidden; }
.card::before {
  content: ""; position: absolute; top: 0; left: 0; right: 0; height: 2px;
  background: var(--accent); transform: scaleX(0); transform-origin: left;
  transition: transform .2s ease;
}
.card:hover::before { transform: scaleX(1); }
.card .meta { transition: letter-spacing .15s ease; }
.card:hover .meta { letter-spacing: .04em; }

/* visual card covers */
.card { padding: 0; }
.cover { height: 84px; display: flex; align-items: center; justify-content: center; }
.cover-glyph { font-family: var(--font-mono); font-size: 32px; font-weight: 600; color: rgba(255,255,255,.92); text-shadow: 0 1px 6px rgba(0,0,0,.18); }
.card-body { padding: 1rem 1.25rem 1.2rem; display: flex; flex-direction: column; }
.card-body h3 { margin: 0 0 .35rem; }

/* big entry blocks (landing) */
.entry-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; margin: 1.25rem 0; }
@media (max-width: 640px) { .entry-grid { grid-template-columns: 1fr; } }
.entry {
  position: relative; overflow: hidden; display: block;
  border: 1px solid var(--color-border-tertiary); border-radius: var(--border-radius-lg);
  background: var(--color-background-primary); padding: 1.7rem 1.7rem 1.5rem;
  transition: transform .15s ease, border-color .15s ease, box-shadow .15s ease;
}
.entry:hover { transform: translateY(-3px); border-color: var(--accent); box-shadow: var(--shadow); text-decoration: none; }
.entry .strip { position: absolute; top: 0; left: 0; right: 0; height: 4px; }
.entry .eico { font-size: 24px; }
.entry h3 { font-size: 20px; margin: .7rem 0 .35rem; }
.entry p { font-size: 14px; color: var(--color-text-secondary); margin: 0 0 .85rem; max-width: 36ch; }
.entry .meta { font-family: var(--font-mono); font-size: 13px; color: var(--accent-text); font-weight: 500; }

/* ---------- structured footer ---------- */
.site-footer {
  margin-top: 5rem; padding-top: 2.25rem;
  border-top: 1px solid var(--color-border-tertiary);
  display: grid; grid-template-columns: 2fr 1fr 1fr; gap: 1.5rem 2rem;
}
.site-footer .fbrand { font-weight: 600; display: inline-flex; align-items: center; gap: .5rem; font-size: 15px; }
.site-footer .ftag { margin: .6rem 0 0; font-size: 13px; color: var(--color-text-tertiary); max-width: 36ch; line-height: 1.6; }
.site-footer h4 { font-size: 12px; text-transform: uppercase; letter-spacing: .07em; color: var(--color-text-tertiary); margin: .1rem 0 .7rem; font-weight: 600; }
.site-footer .flink { display: block; font-size: 14px; color: var(--color-text-secondary); margin: .4rem 0; }
.site-footer .flink:hover { color: var(--accent-text); text-decoration: none; }
.footer-bottom {
  grid-column: 1 / -1; margin-top: 1.5rem; padding-top: 1.25rem;
  border-top: 1px solid var(--color-border-tertiary);
  font-size: 12px; color: var(--color-text-tertiary);
  display: flex; justify-content: space-between; flex-wrap: wrap; gap: .5rem;
}
@media (max-width: 620px) {
  .site-footer { grid-template-columns: 1fr 1fr; }
  .site-footer > div:first-child { grid-column: 1 / -1; }
}

/* ---------- article (concept viewer) ---------- */
.article { max-width: 760px; }
.article h1 { font-size: 30px; font-weight: 700; letter-spacing: -.02em; }
.article h2 { font-size: 21px; margin-top: 2.25rem; }
.article h3 { font-size: 16px; margin-top: 1.5rem; }
.article pre {
  background: var(--color-background-secondary); padding: 1rem 1.1rem;
  border-radius: var(--border-radius-md); overflow: auto;
  border: 1px solid var(--color-border-tertiary);
}
.article pre code { background: none; padding: 0; font-size: 13px; }
.article table { border-collapse: collapse; width: 100%; margin: 1rem 0; }
.article th, .article td { border: 1px solid var(--color-border-tertiary); padding: 7px 11px; text-align: left; font-size: 14px; }
.article th { background: var(--color-background-secondary); }
.article blockquote {
  border-left: 3px solid var(--accent); margin: 1rem 0; padding: .4rem 1rem;
  color: var(--color-text-secondary); background: var(--color-background-secondary);
  border-radius: 0 var(--border-radius-md) var(--border-radius-md) 0;
}
.article img { max-width: 100%; }