:root {
  color-scheme: light;
  --ink: #17202a;
  --muted: #5d6875;
  --line: #dfe5ea;
  --paper: #fbfcfd;
  --panel: #ffffff;
  --accent: #276749;
  --accent-soft: #e6f4ec;
  --warm: #fff7e6;
  --warm-line: #f0c36a;
  --code: #f1f4f6;
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body { margin: 0; color: var(--ink); background: var(--paper); line-height: 1.65; }
a { color: var(--accent); }
.shell { display: grid; grid-template-columns: minmax(190px, 240px) minmax(0, 780px); gap: 3rem; max-width: 1160px; margin: 0 auto; padding: 3rem 1.5rem 5rem; }
.toc { position: sticky; top: 1.5rem; align-self: start; font-size: .92rem; }
.toc strong { display: block; margin-bottom: .7rem; }
.toc a { display: block; padding: .28rem 0; text-decoration: none; color: var(--muted); }
.toc a:hover { color: var(--accent); }
main { min-width: 0; }
.kicker { color: var(--accent); font-size: .78rem; font-weight: 750; letter-spacing: .12em; text-transform: uppercase; }
.meta { color: var(--muted); font-size: .92rem; }
.nav-row { display: flex; justify-content: space-between; gap: 1rem; margin-top: 2rem; }
.nav-row a { max-width: 48%; }
.small { font-size: .9rem; color: var(--muted); }
h1 { max-width: 760px; margin: .4rem 0 1rem; font-size: clamp(2rem, 5vw, 3.5rem); line-height: 1.08; letter-spacing: -.04em; }
h2 { margin-top: 3rem; padding-top: 1rem; border-top: 1px solid var(--line); font-size: 1.65rem; line-height: 1.2; }
h3 { margin-top: 1.8rem; font-size: 1.1rem; }
.lede { color: var(--muted); font-size: 1.1rem; }
.callout, .card, .question { background: var(--panel); border: 1px solid var(--line); border-radius: 12px; padding: 1.1rem 1.25rem; margin: 1.1rem 0; }
.callout { background: var(--accent-soft); border-color: #b7ddc5; }
.warm { background: var(--warm); border-color: var(--warm-line); }
.grid { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 1rem; }
table { width: 100%; border-collapse: collapse; margin: 1rem 0; font-size: .95rem; }
th, td { text-align: left; vertical-align: top; padding: .7rem; border-bottom: 1px solid var(--line); }
th { background: var(--code); }
code { background: var(--code); border-radius: 4px; padding: .1rem .3rem; }
pre { overflow-x: auto; padding: 1rem; background: #182027; color: #eef4f6; border-radius: 10px; }
pre code { background: transparent; color: inherit; padding: 0; }
li { margin: .35rem 0; }
.question legend { font-weight: 700; }
.options { display: flex; flex-wrap: wrap; gap: .5rem; margin-top: .75rem; }
button { border: 1px solid #b7c2ca; border-radius: 7px; padding: .55rem .75rem; background: #fff; color: var(--ink); cursor: pointer; font: inherit; }
button:hover { border-color: var(--accent); color: var(--accent); }
button.correct { border-color: #2f855a; background: #e6f4ec; }
button.incorrect { border-color: #c53030; background: #fff0f0; }
.feedback { min-height: 1.5em; margin: .75rem 0 0; font-weight: 650; }
footer { margin-top: 4rem; padding-top: 1rem; border-top: 1px solid var(--line); color: var(--muted); font-size: .9rem; }
@media (max-width: 760px) {
  .shell { display: block; padding: 1.4rem 1rem 3rem; }
  .toc { position: static; padding: .8rem 0 1.2rem; border-bottom: 1px solid var(--line); }
  .grid { grid-template-columns: 1fr; }
  table { font-size: .87rem; }
  th, td { padding: .5rem; }
}