:root {
  --bg: #f4f5f8;
  --surface: #ffffff;
  --text: #16181d;
  --muted: #5b6270;
  --brand: #0b1f4d;
  --link: #1f4fbf;
  --line: #dfe3ea;
  --fill: #fff1b8;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0e1116;
    --surface: #171b22;
    --text: #e8eaee;
    --muted: #a0a7b4;
    --brand: #0b1f4d;
    --link: #8fb0ff;
    --line: #2a303b;
    --fill: #5a4a00;
  }
}
* { box-sizing: border-box; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font: 17px/1.6 -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
}
.bar {
  background: var(--brand);
  color: #fff;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  padding: 12px 16px;
}
.brand { display: flex; align-items: center; gap: 10px; color: #fff; text-decoration: none; font-weight: 700; font-size: 20px; }
.brand img { border-radius: 8px; }
nav { display: flex; gap: 16px; }
nav a { color: #cdd6ee; text-decoration: none; font-weight: 600; }
nav a[aria-current="page"] { color: #fff; }
main {
  max-width: 760px;
  margin: 24px auto;
  padding: 24px 16px 32px;
  background: var(--surface);
  border-radius: 16px;
}
@media (min-width: 800px) { main { padding: 40px 48px; margin: 40px auto; } }
h1 { font-size: 32px; line-height: 1.2; margin: 0 0 4px; }
h2 { font-size: 22px; margin: 36px 0 8px; }
h3 { font-size: 17px; margin: 20px 0 4px; }
.meta { color: var(--muted); margin: 0 0 20px; }
.lead { font-size: 19px; }
a { color: var(--link); }
ul { padding-left: 22px; }
li { margin: 4px 0; }
.table-wrap { overflow-x: auto; }
table { width: 100%; border-collapse: collapse; font-size: 15px; }
th, td { text-align: left; vertical-align: top; padding: 10px 8px; border-bottom: 1px solid var(--line); }
th { color: var(--muted); font-weight: 600; }
.fill { background: var(--fill); padding: 0 4px; border-radius: 4px; }
footer { max-width: 760px; margin: 0 auto 40px; padding: 0 16px; color: var(--muted); font-size: 14px; text-align: center; }

/* Navigation wraps on phones */
.bar { flex-wrap: wrap; }
nav { flex-wrap: wrap; gap: 4px 16px; }

/* Home page */
.hero { text-align: center; padding: 8px 0 8px; }
.hero img { border-radius: 22px; }
.hero h1 { margin-top: 12px; }
.buttons { display: flex; flex-wrap: wrap; gap: 12px; justify-content: center; margin: 20px 0 8px; }
.btn { display: inline-block; padding: 12px 20px; border-radius: 12px; background: var(--brand); color: #fff; text-decoration: none; font-weight: 700; border: 0; font: inherit; font-weight: 700; cursor: pointer; }
.btn.secondary { background: transparent; color: var(--link); border: 1.5px solid var(--line); }
.btn[aria-disabled="true"] { opacity: .55; pointer-events: none; }
.note { color: var(--muted); font-size: 14px; text-align: center; margin: 4px 0 0; }
.cards { display: grid; grid-template-columns: repeat(auto-fit, minmax(200px, 1fr)); gap: 12px; margin: 16px 0; }
.card { display: block; border: 1px solid var(--line); border-radius: 14px; padding: 16px; color: var(--text); text-decoration: none; }
.card strong { display: block; color: var(--link); margin-bottom: 4px; }
.card span { color: var(--muted); font-size: 15px; }
.facts { display: grid; grid-template-columns: repeat(auto-fit, minmax(140px, 1fr)); gap: 12px; margin: 16px 0; }
.fact { border: 1px solid var(--line); border-radius: 14px; padding: 14px; text-align: center; }
.fact b { display: block; font-size: 26px; color: var(--link); }
.fact span { color: var(--muted); font-size: 14px; }
.callout { border-left: 4px solid var(--link); background: var(--bg); padding: 12px 16px; border-radius: 0 12px 12px 0; margin: 20px 0; }

/* Ad slots: empty until AdSense is approved */
.ad { margin: 28px 0; min-height: 0; }

/* Practice quiz */
.quiz-progress { color: var(--muted); font-size: 15px; margin: 0 0 8px; }
.quiz-q { font-size: 20px; font-weight: 600; margin: 8px 0 16px; }
.opts { display: grid; gap: 10px; }
.opt { text-align: left; padding: 14px 16px; border-radius: 12px; border: 1.5px solid var(--line); background: var(--surface); color: var(--text); font: inherit; cursor: pointer; }
.opt[aria-pressed="true"] { border-color: var(--link); }
.opt.right { border-color: #1e8e3e; background: rgba(30,142,62,.12); }
.opt.wrong { border-color: #c5221f; background: rgba(197,34,31,.12); }
.opt:disabled { cursor: default; }
.explain { margin: 16px 0 0; padding: 14px 16px; border-radius: 12px; background: var(--bg); }
.quiz-actions { display: flex; gap: 12px; flex-wrap: wrap; margin-top: 18px; }
.score { font-size: 40px; font-weight: 800; margin: 8px 0; }

/* App store badges */
.stores { display: flex; flex-wrap: wrap; gap: 12px; justify-content: center; margin: 20px 0 8px; }
.store { display: inline-flex; flex-direction: column; justify-content: center; min-width: 170px; padding: 8px 18px; border-radius: 12px; background: #000; color: #fff; text-decoration: none; font-weight: 700; font-size: 20px; line-height: 1.15; }
.store small { font-size: 12px; font-weight: 500; opacity: .85; }
.store[aria-disabled="true"] { opacity: .6; cursor: default; }
@media (prefers-color-scheme: dark) { .store { background: #fff; color: #000; } }

/* Practice mode picker */
.chips { display: flex; flex-wrap: wrap; gap: 8px; margin: 0 0 20px; }
.chip { padding: 6px 12px; border-radius: 999px; border: 1.5px solid var(--line); color: var(--text); text-decoration: none; font-size: 15px; font-weight: 600; }
.chip[aria-current="page"] { background: var(--brand); border-color: var(--brand); color: #fff; }