/* Shared stylesheet for the AI Engineer interview study guide. */
:root {
  --bg: #fbfaf7;
  --surface: #ffffff;
  --surface-2: #f3f1ec;
  --text: #1d1f23;
  --muted: #5d636e;
  --border: #e3e0d8;
  --accent: #2f5bd3;
  --accent-soft: #e7edfc;
  --track-a: #7a3fd1;   /* model internals */
  --track-b: #0f8a6b;   /* product engineering */
  --track-c: #b5541c;   /* design interviews */
  --warn: #a65d00;
  --warn-soft: #fff4e2;
  --good-soft: #e6f6ef;
  --code-bg: #f4f2ee;
  --mono: ui-monospace, "SF Mono", Menlo, Consolas, monospace;
  --sans: -apple-system, BlinkMacSystemFont, "Inter", "Segoe UI", Roboto, sans-serif;
  --serif: "Iowan Old Style", "Charter", Georgia, serif;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #15171b;
    --surface: #1c1f24;
    --surface-2: #23272e;
    --text: #e6e7ea;
    --muted: #9aa1ad;
    --border: #2f343c;
    --accent: #8fb0ff;
    --accent-soft: #23304d;
    --track-a: #b896f5;
    --track-b: #5fd3b1;
    --track-c: #f0a070;
    --warn: #ffb35c;
    --warn-soft: #3a2c17;
    --good-soft: #17352b;
    --code-bg: #23272e;
  }
}
* { box-sizing: border-box; }
html { scroll-behavior: smooth; scroll-padding-top: 16px; }
body {
  margin: 0; background: var(--bg); color: var(--text);
  font-family: var(--sans); font-size: 16.5px; line-height: 1.65;
  -webkit-font-smoothing: antialiased;
}
a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

/* ---------- layout ---------- */
.layout { display: grid; grid-template-columns: 280px minmax(0, 1fr); max-width: 1320px; margin: 0 auto; }
nav.toc {
  position: sticky; top: 0; height: 100vh; overflow-y: auto;
  padding: 24px 18px 40px 24px; border-right: 1px solid var(--border); font-size: 13.5px;
}
nav.toc .home { display: block; font-weight: 600; margin-bottom: 14px; color: var(--muted); }
nav.toc .toc-title { font-size: 11px; text-transform: uppercase; letter-spacing: .08em; color: var(--muted); margin: 8px 0; }
nav.toc ol { list-style: none; padding: 0; margin: 0; }
nav.toc li a { display: block; padding: 3px 8px; border-radius: 6px; color: var(--text); line-height: 1.35; }
nav.toc li a:hover { background: var(--surface-2); text-decoration: none; }
nav.toc li a.active { background: var(--accent-soft); color: var(--accent); }
nav.toc li.h3 a { padding-left: 22px; color: var(--muted); font-size: 12.5px; }
main { padding: 40px 56px 120px; max-width: 920px; min-width: 0; overflow-wrap: break-word; }
nav.toc .toc-toggle { display: none; }
@media (max-width: 960px) {
  /* minmax(0, …) stops a wide table or code block from stretching the page */
  .layout { grid-template-columns: minmax(0, 1fr); }
  /* the contents list collapses into a sticky bar with a toggle (built in page.js) */
  nav.toc {
    position: sticky; top: 0; z-index: 20; height: auto; overflow: visible;
    padding: 8px 16px; border-right: 0; border-bottom: 1px solid var(--border);
    background: var(--bg); display: flex; align-items: center; gap: 12px;
  }
  nav.toc .home { margin: 0; font-size: 13px; white-space: nowrap; }
  nav.toc .toc-title { display: none; }
  nav.toc .toc-toggle {
    display: inline-flex; align-items: center; gap: 6px; margin-left: auto;
    font: 600 13px var(--sans); color: var(--text); background: var(--surface);
    border: 1px solid var(--border); border-radius: 8px; padding: 6px 12px; cursor: pointer;
  }
  nav.toc ol {
    display: none; position: absolute; left: 0; right: 0; top: 100%;
    max-height: 70vh; overflow-y: auto; padding: 8px 12px 16px;
    background: var(--bg); border-bottom: 1px solid var(--border);
    box-shadow: 0 8px 24px rgba(0, 0, 0, .12); font-size: 14px;
  }
  nav.toc.open ol { display: block; }
  nav.toc li a { padding: 7px 8px; }
  main { padding: 20px 16px 80px; }
  html { scroll-padding-top: 60px; }
}
@media (max-width: 600px) {
  body { font-size: 16px; line-height: 1.6; }
  h1 { font-size: 1.75rem; }
  h2 { font-size: 1.35rem; margin-top: 40px; }
  h3 { font-size: 1.08rem; }
  .lede { font-size: 1.02rem; }
  /* any table not already in a .table-wrap scrolls on its own instead of widening the page */
  main table { display: block; overflow-x: auto; -webkit-overflow-scrolling: touch; }
  th, td { padding: 6px 8px; font-size: 13.5px; }
  pre, .flow { font-size: 12px; padding: 10px 12px; }
  .callout, .tldr, .further, details.qa { padding-left: 12px; padding-right: 12px; }
  .hub { padding: 28px 16px 80px; }
  .pager { flex-direction: column; }
  /* wide diagrams keep a readable size and scroll sideways */
  .svg-scroll { overflow-x: auto; -webkit-overflow-scrolling: touch; }
  main svg.wide-svg { min-width: 600px; max-width: none; }
  /* long inline formulas can't wrap; let each one scroll on its own */
  main .katex { display: inline-block; max-width: 100%; overflow-x: auto; overflow-y: hidden; vertical-align: middle; }
  main .katex-display > .katex { display: block; }
}
/* safety nets for content written by different authors */
main svg { max-width: 100%; height: auto; }
main img { max-width: 100%; height: auto; }
main pre, main .flow { max-width: 100%; }
main .katex-display { overflow-x: auto; overflow-y: hidden; padding: 4px 0; }
/* KaTeX's hidden MathML copy is position:absolute; anchor it so it can't escape scroll boxes and widen the page */
main .katex, .table-wrap, main pre, main .flow { position: relative; }
main p code, main li code, main td code { overflow-wrap: anywhere; }
main a { overflow-wrap: anywhere; }

/* ---------- typography ---------- */
h1 { font-family: var(--serif); font-size: 2.3rem; line-height: 1.15; margin: 0 0 8px; }
h2 { font-family: var(--serif); font-size: 1.65rem; margin: 56px 0 12px; padding-top: 12px; border-top: 1px solid var(--border); }
h3 { font-size: 1.15rem; margin: 32px 0 8px; }
h4 { font-size: 1rem; margin: 22px 0 6px; color: var(--muted); text-transform: uppercase; letter-spacing: .04em; font-size: .82rem; }
p, ul, ol { margin: 0 0 14px; }
li { margin-bottom: 4px; }
strong { font-weight: 650; }
code { font-family: var(--mono); font-size: .88em; background: var(--code-bg); padding: 1px 5px; border-radius: 4px; }
pre { background: var(--code-bg); border: 1px solid var(--border); padding: 14px 16px; border-radius: 8px; overflow-x: auto; font-size: 13.5px; line-height: 1.5; }
pre code { background: none; padding: 0; }
.lede { font-size: 1.12rem; color: var(--muted); margin-bottom: 20px; }
.track-tag { display: inline-block; font-size: 11px; font-weight: 700; letter-spacing: .08em; text-transform: uppercase; padding: 3px 9px; border-radius: 999px; margin-bottom: 14px; }
.track-tag.a { color: var(--track-a); border: 1px solid var(--track-a); }
.track-tag.b { color: var(--track-b); border: 1px solid var(--track-b); }
.track-tag.c { color: var(--track-c); border: 1px solid var(--track-c); }

/* ---------- tables ---------- */
.table-wrap { overflow-x: auto; margin: 0 0 18px; }
table { border-collapse: collapse; width: 100%; font-size: 14.5px; background: var(--surface); }
th, td { border: 1px solid var(--border); padding: 8px 10px; text-align: left; vertical-align: top; }
th { background: var(--surface-2); font-weight: 650; }

/* ---------- callouts ---------- */
.callout { border: 1px solid var(--border); border-left: 4px solid var(--accent); background: var(--surface); padding: 12px 16px; border-radius: 8px; margin: 18px 0; }
.callout > :last-child { margin-bottom: 0; }
.callout .label { display: block; font-size: 11px; font-weight: 700; letter-spacing: .08em; text-transform: uppercase; color: var(--accent); margin-bottom: 4px; }
.callout.interview { border-left-color: var(--track-b); background: var(--good-soft); }
.callout.interview .label { color: var(--track-b); }
.callout.intuition { border-left-color: var(--track-a); }
.callout.intuition .label { color: var(--track-a); }
.callout.verify { border-left-color: var(--warn); background: var(--warn-soft); }
.callout.verify .label { color: var(--warn); }
.callout.pitfall { border-left-color: #d14343; }
.callout.pitfall .label { color: #d14343; }

/* tldr box at top of page */
.tldr { background: var(--surface); border: 1px solid var(--border); border-radius: 10px; padding: 16px 20px; margin: 20px 0 8px; }
.tldr h3 { margin-top: 0; font-size: .85rem; text-transform: uppercase; letter-spacing: .08em; color: var(--muted); }

/* ---------- sources ---------- */
/* inline source chip placed right after a claim: <a class="src" href="...">[Vaswani+ 2017]</a> */
a.src { font-size: .74em; font-family: var(--mono); color: var(--muted); border: 1px solid var(--border); border-radius: 4px; padding: 0 4px; margin-left: 3px; white-space: nowrap; vertical-align: 1px; }
a.src:hover { color: var(--accent); border-color: var(--accent); text-decoration: none; }
/* flag for numbers that should be double-checked */
.approx { border-bottom: 1px dashed var(--warn); cursor: help; }
.further { font-size: 14px; background: var(--surface-2); border-radius: 8px; padding: 10px 14px; margin: 14px 0; }
.further strong { font-size: 11px; letter-spacing: .08em; text-transform: uppercase; color: var(--muted); display: block; margin-bottom: 4px; }
.further ul { margin: 0; padding-left: 18px; }

/* ---------- diagrams ---------- */
figure { margin: 20px 0; }
figure svg { max-width: 100%; height: auto; display: block; margin: 0 auto; }
figcaption { font-size: 13px; color: var(--muted); text-align: center; margin-top: 6px; }
.flow { font-family: var(--mono); font-size: 13px; white-space: pre; overflow-x: auto; background: var(--surface); border: 1px solid var(--border); padding: 14px; border-radius: 8px; line-height: 1.45; }

/* ---------- Q&A ---------- */
details.qa { border: 1px solid var(--border); background: var(--surface); border-radius: 8px; padding: 10px 14px; margin: 8px 0; }
details.qa summary { cursor: pointer; font-weight: 600; }
details.qa[open] summary { margin-bottom: 8px; }
details.qa > :last-child { margin-bottom: 0; }

/* two-column comparison cards */
.grid2 { display: grid; grid-template-columns: 1fr 1fr; gap: 14px; margin: 16px 0; }
.card { background: var(--surface); border: 1px solid var(--border); border-radius: 10px; padding: 14px 16px; }
.card h4 { margin-top: 0; }
.card > :last-child { margin-bottom: 0; }
@media (max-width: 700px) { .grid2 { grid-template-columns: 1fr; } }

/* ---------- hub page ---------- */
.hub { max-width: 1080px; margin: 0 auto; padding: 48px 24px 100px; }
.hub-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(300px, 1fr)); gap: 16px; margin: 18px 0 40px; }
.hub-card { display: block; background: var(--surface); border: 1px solid var(--border); border-radius: 12px; padding: 18px 20px; color: var(--text); transition: border-color .15s, transform .15s; }
.hub-card:hover { text-decoration: none; border-color: var(--accent); transform: translateY(-2px); }
.hub-card .num { font-family: var(--mono); font-size: 12px; color: var(--muted); }
.hub-card h3 { margin: 4px 0 6px; font-size: 1.1rem; }
.hub-card p { font-size: 14px; color: var(--muted); margin: 0; }
.hub h2.a { color: var(--track-a); border-top-color: var(--track-a); }
.hub h2.b { color: var(--track-b); border-top-color: var(--track-b); }
.hub h2.c { color: var(--track-c); border-top-color: var(--track-c); }

.pager { display: flex; justify-content: space-between; gap: 12px; margin-top: 60px; padding-top: 20px; border-top: 1px solid var(--border); font-size: 14px; }