/* PrepToExcel site styles
   Layout: single centred column (max 1100px) with card grids; serif display for headings, sans for body.
   Palette: deep ink-blue brand, amber accent (matches favicon), cool neutrals. Light + dark themes. */
:root {
  --bg: #f6f7f9;
  --surface: #ffffff;
  --ink: #17212b;
  --muted: #56636f;
  --line: #d9dfe5;
  --brand: #14466e;
  --brand-ink: #ffffff;
  --accent: #c47a12;
  --accent-soft: #fff4e0;
  --link: #165a8f;
  --f-display: "Source Serif 4", Georgia, "Times New Roman", serif;
  --f-body: "Public Sans", -apple-system, "Segoe UI", Arial, sans-serif;
  --radius: 10px;
  color-scheme: light;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0f151b; --surface: #17202a; --ink: #e6ebef; --muted: #a2adb7; --line: #2b3742;
    --brand: #6aa8dd; --brand-ink: #0f151b; --accent: #f2b155; --accent-soft: #2a2316; --link: #8cc0ea;
    color-scheme: dark;
  }
}
*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body { margin: 0; background: var(--bg); color: var(--ink); font: 17px/1.6 var(--f-body); }
img { max-width: 100%; height: auto; }
a { color: var(--link); }
a:focus-visible, button:focus-visible { outline: 3px solid var(--accent); outline-offset: 2px; }
.skip { position: absolute; left: -9999px; }
.skip:focus { left: 16px; top: 16px; background: var(--surface); padding: 8px 12px; z-index: 10; }

.wrap { max-width: 1100px; margin: 0 auto; padding-left: max(20px, env(safe-area-inset-left)); padding-right: max(20px, env(safe-area-inset-right)); }

/* header */
.site-header { background: var(--surface); border-bottom: 1px solid var(--line); }
.bar { display: flex; align-items: center; justify-content: space-between; gap: 16px; flex-wrap: wrap; padding-block: 14px; }
.logo { display: inline-flex; align-items: center; gap: 10px; font: 700 20px/1 var(--f-display); color: var(--ink); text-decoration: none; }
.logo-mark { display: grid; place-items: center; width: 32px; height: 32px; border-radius: 8px; background: var(--brand); color: var(--brand-ink); font: 700 18px/1 var(--f-body); }
.site-header ul { display: flex; gap: 20px; list-style: none; margin: 0; padding: 0; flex-wrap: wrap; }
.site-header nav a { color: var(--muted); text-decoration: none; font-weight: 600; font-size: 15px; }
.site-header nav a:hover, .site-header nav a[aria-current="page"] { color: var(--ink); }

/* type */
h1, h2, h3 { font-family: var(--f-display); line-height: 1.2; text-wrap: balance; }
h1 { font-size: clamp(30px, 4.5vw, 46px); margin: 0 0 12px; }
h2 { font-size: clamp(22px, 3vw, 28px); margin: 0 0 14px; }
h3 { font-size: 20px; }
.lede { font-size: 19px; color: var(--muted); max-width: 62ch; margin: 0 0 20px; }
.eyebrow { text-transform: uppercase; letter-spacing: .08em; font-size: 12.5px; font-weight: 700; color: var(--accent); margin: 0 0 8px; }

.hero { padding-block: 64px 40px; }
.hero h1 { max-width: 18ch; }
.page-hero { padding-block: 8px 12px; }
.block { padding-block: 24px; }
.page { padding-block: 40px 56px; }
main > .wrap { padding-bottom: 48px; }

/* buttons */
.btn { display: inline-block; background: var(--brand); color: var(--brand-ink); text-decoration: none; font-weight: 700; padding: 13px 22px; border-radius: 8px; }
.btn:hover { filter: brightness(1.08); }

/* cards */
.cards { display: grid; grid-template-columns: repeat(auto-fill, minmax(min(100%, 300px), 1fr)); gap: 16px; }
.card { display: flex; flex-direction: column; gap: 6px; background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius); padding: 20px; text-decoration: none; color: var(--ink); transition: border-color .15s, transform .15s; }
.card:hover { border-color: var(--brand); transform: translateY(-2px); }
.card-eyebrow { font-size: 12.5px; text-transform: uppercase; letter-spacing: .07em; color: var(--muted); font-weight: 700; }
.card-title { font: 700 21px/1.25 var(--f-display); }
.card-text { color: var(--muted); font-size: 15.5px; }
.card-cta { margin-top: auto; padding-top: 8px; color: var(--link); font-weight: 700; font-size: 15px; }

/* lesson list */
.lesson-list { list-style: none; margin: 0; padding: 0; border-top: 1px solid var(--line); }
.lesson-list li { display: flex; flex-direction: column; gap: 2px; padding: 14px 0; border-bottom: 1px solid var(--line); }
.lesson-list a { font-weight: 700; font-size: 17.5px; }
.lesson-list span { color: var(--muted); font-size: 15px; }

/* facts */
.facts { display: grid; grid-template-columns: repeat(auto-fit, minmax(160px, 1fr)); gap: 10px; margin: 0 0 22px; max-width: 760px; }
.facts div { background: var(--surface); border: 1px solid var(--line); border-radius: 8px; padding: 10px 14px; }
.facts dt { font-size: 12.5px; text-transform: uppercase; letter-spacing: .07em; color: var(--muted); font-weight: 700; }
.facts dd { margin: 2px 0 0; font-weight: 700; font-variant-numeric: tabular-nums; }

/* prose */
.prose { max-width: 72ch; }
.prose h2 { margin-top: 36px; }
.prose table { border-collapse: collapse; width: 100%; margin: 14px 0 20px; font-size: 15.5px; display: block; overflow-x: auto; }
.prose th, .prose td { border: 1px solid var(--line); padding: 8px 12px; text-align: left; }
.prose th { background: var(--surface); }
.prose blockquote { margin: 14px 0; padding: 10px 16px; background: var(--accent-soft); border-left: 4px solid var(--accent); border-radius: 0 8px 8px 0; }
.prose blockquote p { margin: 0; }
.prose code { background: var(--surface); border: 1px solid var(--line); border-radius: 4px; padding: 1px 5px; font-size: .92em; }

.crumbs { font-size: 14.5px; color: var(--muted); padding-top: 24px; margin-bottom: 14px; display: flex; gap: 6px; flex-wrap: wrap; }
.callout { background: var(--accent-soft); border: 1px solid var(--line); border-radius: var(--radius); padding: 14px 18px; margin: 28px 0; max-width: 72ch; }
.callout p { margin: 0; }
.pager { display: flex; justify-content: space-between; gap: 16px; flex-wrap: wrap; border-top: 1px solid var(--line); padding-top: 18px; max-width: 72ch; }
.pager a { font-weight: 700; text-decoration: none; }

/* footer */
.site-footer { background: var(--surface); border-top: 1px solid var(--line); padding-block: 32px; font-size: 14.5px; color: var(--muted); }
.foot-brand { font: 700 18px/1 var(--f-display); color: var(--ink); margin: 0 0 12px; }
.foot-links { list-style: none; display: flex; flex-wrap: wrap; gap: 18px; padding: 0; margin: 0 0 14px; }
.foot-note { max-width: 80ch; margin: 0 0 6px; }

@media (prefers-reduced-motion: reduce) { .card { transition: none; } .card:hover { transform: none; } }

/* list breathing room */
.prose ul, .prose ol { padding-left: 1.3em; margin: 14px 0 24px; }
.prose li { margin-bottom: 16px; padding-left: 4px; }
.prose li:last-child { margin-bottom: 0; }
.prose li::marker { color: var(--accent); }
.prose ul.topics { columns: 2 260px; column-gap: 40px; }
.prose ul.topics li { margin-bottom: 10px; break-inside: avoid; }
.prose h2 + p, .prose h2 + ul { margin-top: 0; }