:root {
  --bg: #f7f7f5;
  --surface: #ffffff;
  --surface-2: #f0f0ec;
  --text: #1c1d21;
  --muted: #5f6269;
  --border: #e2e2dc;
  --link: #1f5fbf;
  --algo: #2f6fdf;
  --ds: #0f9a6c;
  --arch: #c87a05;
  --os: #8a4fd8;
  --accent: var(--link);
  --radius: 12px;
  --mono: ui-monospace, "SF Mono", SFMono-Regular, Menlo, Consolas, monospace;
  --sans: -apple-system, BlinkMacSystemFont, "Segoe UI", system-ui, Roboto, "Helvetica Neue", Arial, sans-serif;
  color-scheme: light dark;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #111318;
    --surface: #181b21;
    --surface-2: #20242c;
    --text: #e6e7ea;
    --muted: #9aa0aa;
    --border: #2b3039;
    --link: #7fb0ff;
    --algo: #6ea0ff;
    --ds: #3ccf9a;
    --arch: #f2a93b;
    --os: #b98cff;
  }
}

* { box-sizing: border-box; }

html { -webkit-text-size-adjust: 100%; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font: 17px/1.65 var(--sans);
  padding: 0 max(16px, env(safe-area-inset-left)) 64px max(16px, env(safe-area-inset-right));
}

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

.topbar {
  max-width: 760px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  padding: max(14px, env(safe-area-inset-top)) 0 14px;
}
.brand { font-weight: 800; letter-spacing: -0.02em; color: var(--text); font-size: 18px; }
.brand span { color: var(--muted); font-weight: 500; margin-left: 4px; }
.topbar nav { display: flex; gap: 16px; font-size: 15px; }
.topbar nav a { color: var(--muted); }
.topbar nav a:hover { color: var(--text); text-decoration: none; }

main { max-width: 760px; margin: 0 auto; }
.status { color: var(--muted); padding: 48px 0; text-align: center; }

/* ---------- card header ---------- */
.track-algo { --accent: var(--algo); }
.track-ds   { --accent: var(--ds); }
.track-arch { --accent: var(--arch); }
.track-os   { --accent: var(--os); }

.card-head {
  border-top: 4px solid var(--accent);
  background: var(--surface);
  border-radius: var(--radius);
  padding: 22px 22px 20px;
  margin: 8px 0 20px;
  box-shadow: 0 1px 0 var(--border);
}
.meta { display: flex; flex-wrap: wrap; align-items: center; gap: 8px 12px; font-size: 13.5px; color: var(--muted); }
.badge {
  display: inline-block;
  font: 700 11.5px/1 var(--sans);
  letter-spacing: 0.06em;
  color: #fff;
  background: var(--accent);
  border-radius: 6px;
  padding: 5px 7px;
}
@media (prefers-color-scheme: dark) { .badge { color: #111318; } }
.card-head h1 { font-size: clamp(25px, 5.2vw, 34px); line-height: 1.2; letter-spacing: -0.02em; margin: 12px 0 10px; }
.tagline { font-size: 18px; color: var(--muted); margin: 0; }

.toc { display: flex; flex-wrap: wrap; gap: 8px; margin: 16px 0 0; padding: 0; list-style: none; }
.toc a {
  display: inline-block; font-size: 13.5px; color: var(--text);
  background: var(--surface-2); border-radius: 999px; padding: 4px 11px;
}
.toc a:hover { text-decoration: none; background: var(--border); }

/* ---------- blocks ---------- */
.block {
  background: var(--surface);
  border-radius: var(--radius);
  padding: 4px 22px 18px;
  margin: 0 0 16px;
  box-shadow: 0 1px 0 var(--border);
  scroll-margin-top: 12px;
}
.block > h2 {
  font-size: 13px; text-transform: uppercase; letter-spacing: 0.08em;
  color: var(--accent); margin: 18px 0 8px;
}
.block.prose > h2 { font-size: 22px; text-transform: none; letter-spacing: -0.01em; color: var(--text); }

.tldr { border-left: 4px solid var(--accent); }
.keypoints ul { margin: 6px 0 0; padding-left: 20px; }
.keypoints li { margin: 6px 0; }
.keypoints li::marker { color: var(--accent); }

.md p, .md ul, .md ol { margin: 10px 0; }
.md li { margin: 5px 0; }
.md h3, .md h4 { margin: 20px 0 6px; line-height: 1.3; }
.md strong { font-weight: 650; }
.md blockquote { margin: 12px 0; padding: 2px 14px; border-left: 3px solid var(--border); color: var(--muted); }
.md :not(pre) > code {
  font: 0.86em var(--mono); background: var(--surface-2);
  padding: 0.12em 0.35em; border-radius: 5px; white-space: nowrap;
}

pre {
  margin: 12px 0; border-radius: 10px; overflow-x: auto;
  background: var(--surface-2); border: 1px solid var(--border);
}
pre code, pre code.hljs {
  display: block; padding: 14px 16px; font: 13.5px/1.55 var(--mono);
  background: transparent; white-space: pre; tab-size: 4;
}
figure.code { margin: 0; }
figure.code figcaption { font-size: 14px; color: var(--muted); margin: 4px 0 0; }

.table-wrap { overflow-x: auto; margin: 12px 0; -webkit-overflow-scrolling: touch; }
table { border-collapse: collapse; width: 100%; font-size: 14.5px; }
th, td { text-align: left; padding: 8px 10px; border-bottom: 1px solid var(--border); vertical-align: top; }
th { font-size: 12.5px; text-transform: uppercase; letter-spacing: 0.05em; color: var(--muted); white-space: nowrap; }
td code { white-space: nowrap; }

.katex { font-size: 1.05em; }
.katex-display { overflow-x: auto; overflow-y: hidden; padding: 4px 0; margin: 14px 0; }

details { border-top: 1px solid var(--border); padding: 10px 0; }
details:first-of-type { border-top: none; }
summary { cursor: pointer; font-weight: 600; list-style: none; position: relative; padding-left: 22px; }
summary::-webkit-details-marker { display: none; }
summary::before {
  content: "›"; position: absolute; left: 4px; top: -1px; color: var(--accent);
  font-size: 20px; line-height: 1.4; transition: transform 0.15s;
}
details[open] > summary::before { transform: rotate(90deg); }
summary .md p { display: inline; margin: 0; }
.answer { padding: 6px 0 0 22px; }
.q-kind { font-size: 12px; color: var(--muted); font-weight: 500; margin-left: 6px; }

.chips { display: flex; flex-wrap: wrap; gap: 8px; margin: 8px 0 4px; }
.chip {
  display: inline-flex; align-items: center; gap: 7px; font-size: 14px;
  border: 1px solid var(--border); border-radius: 999px; padding: 4px 12px 4px 6px; color: var(--text);
}
.chip .dot { width: 9px; height: 9px; border-radius: 50%; background: var(--accent); margin-left: 4px; }
a.chip:hover { text-decoration: none; border-color: var(--accent); }
span.chip { color: var(--muted); }

.refs { font-size: 14.5px; color: var(--muted); padding-left: 20px; }

.pager { display: flex; justify-content: space-between; gap: 12px; margin: 24px 0 8px; font-size: 15px; }
.pager a, .pager span { flex: 1; }
.pager .next { text-align: right; }
.pager span { color: var(--muted); opacity: 0.5; }
.gen { text-align: center; font-size: 12.5px; color: var(--muted); margin-top: 18px; }

/* ---------- archive ---------- */
.archive-head h1 { font-size: 28px; margin: 8px 0 4px; letter-spacing: -0.02em; }
.archive-head p { color: var(--muted); margin: 0 0 14px; }
.filters { display: flex; flex-wrap: wrap; gap: 8px; align-items: center; margin-bottom: 14px; }
.filters button {
  font: 600 13px var(--sans); color: var(--text); background: var(--surface);
  border: 1px solid var(--border); border-radius: 999px; padding: 6px 12px; cursor: pointer;
}
.filters button[aria-pressed="true"] { background: var(--accent); border-color: var(--accent); color: #fff; }
@media (prefers-color-scheme: dark) { .filters button[aria-pressed="true"] { color: #111318; } }
.filters input {
  flex: 1 1 180px; min-width: 0; font: 15px var(--sans); color: var(--text);
  background: var(--surface); border: 1px solid var(--border); border-radius: 999px; padding: 7px 14px;
}
.month { font-size: 13px; text-transform: uppercase; letter-spacing: 0.08em; color: var(--muted); margin: 22px 0 8px; }
.entry {
  display: grid; grid-template-columns: 52px 1fr; gap: 12px; align-items: start;
  background: var(--surface); border-radius: var(--radius); padding: 12px 14px; margin-bottom: 8px;
  box-shadow: 0 1px 0 var(--border); color: var(--text); border-left: 4px solid var(--accent);
}
.entry:hover { text-decoration: none; background: var(--surface-2); }
.entry .day { font: 700 20px/1.1 var(--sans); text-align: center; }
.entry .day small { display: block; font-size: 11px; font-weight: 500; color: var(--muted); }
.entry .t { font-weight: 650; line-height: 1.3; }
.entry .s { font-size: 14px; color: var(--muted); margin-top: 3px; line-height: 1.45; }

@media (max-width: 520px) {
  body { font-size: 16px; }
  .card-head, .block { padding-left: 16px; padding-right: 16px; }
  .tagline { font-size: 16.5px; }
  .topbar nav { gap: 12px; }
}

/* Course-grounding blocks ------------------------------------------------ */
.block.metu { border-left: 3px solid var(--accent); padding-left: 1rem; }
.block .hint { margin: -0.25rem 0 0.75rem; font-size: 0.85rem; color: var(--muted); }
.refs.sources .kind {
  display: inline-block; margin-right: 0.45rem; font-size: 0.7rem; letter-spacing: 0.04em;
  text-transform: uppercase; white-space: nowrap; color: var(--muted);
  border: 1px solid var(--border); border-radius: 999px; padding: 0.1rem 0.45rem;
}

@media (max-width: 520px) {
  .katex-display { font-size: 0.92em; text-align: left; }
  .katex-display > .katex { text-align: left; }
}

/* Language toggle ------------------------------------------------------- */
#lang-toggle {
  margin-left: 4px; font: inherit; font-size: 0.8rem; font-weight: 600;
  letter-spacing: 0.04em; color: var(--muted); background: none; cursor: pointer;
  border: 1px solid var(--border); border-radius: 999px; padding: 0.1rem 0.5rem;
}
#lang-toggle:hover { color: var(--text); border-color: var(--muted); }