:root {
  --bg: #f6f7f4; --paper: #ffffff; --ink: #14202b; --soft: #4b5967; --faint: #7a8794; --line: #dfe3dd;
  --sky: #1f5f8b; --sky-2: #e6eff6; --go: #1d7a4f; --go-2: #e3f3ea; --no: #b3372f; --no-2: #fbe9e7; --sun: #f2b33d;
  --radius: 14px; --shadow: 0 1px 2px rgba(20,32,43,.06), 0 8px 24px rgba(20,32,43,.06);
}
@media (prefers-color-scheme: dark) {
  :root { --bg: #0f161c; --paper: #16212a; --ink: #e8eef2; --soft: #b3c0cb; --faint: #8796a3; --line: #263542;
    --sky: #6fb3e6; --sky-2: #172d3d; --go: #5fd39b; --go-2: #12301f; --no: #ff8a80; --no-2: #3a1a17; --sun: #f2b33d; }
}
* { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body { margin: 0; background: var(--bg); color: var(--ink); font: 17px/1.6 "Inter", system-ui, -apple-system, "Segoe UI", Roboto, sans-serif; }
a { color: var(--sky); }
img { max-width: 100%; }
.wrap { max-width: 1040px; margin: 0 auto; padding: 0 20px; }
.narrow { max-width: 760px; }
header.top { border-bottom: 1px solid var(--line); background: var(--paper); }
header.top .wrap { display: flex; align-items: center; justify-content: space-between; gap: 12px; height: 62px; }
.brand { display: flex; align-items: center; gap: 10px; font-weight: 800; letter-spacing: -.01em; color: var(--ink); text-decoration: none; font-size: 19px; }
.brand .mark { width: 30px; height: 30px; border-radius: 8px; background: var(--sky); display: grid; place-items: center; color: #fff; font-size: 13px; font-weight: 800; }
nav.links { display: flex; gap: 18px; align-items: center; font-size: 15px; }
nav.links a { color: var(--soft); text-decoration: none; }
nav.links a:hover { color: var(--ink); }
@media (max-width: 640px) { nav.links .hide-sm { display: none; } }
.btn { display: inline-flex; align-items: center; justify-content: center; gap: 8px; border: 0; border-radius: 999px; padding: 13px 22px;
  font: inherit; font-weight: 700; font-size: 16px; cursor: pointer; text-decoration: none; transition: transform .08s ease, filter .15s ease; }
.btn:active { transform: translateY(1px); }
.btn.primary { background: var(--sky); color: #fff; }
.btn.primary:hover { filter: brightness(1.08); }
.btn.ghost { background: transparent; color: var(--ink); border: 1.5px solid var(--line); }
.btn.go { background: var(--go); color: #fff; }
.btn.small { padding: 9px 16px; font-size: 14.5px; }
.btn[disabled] { opacity: .5; cursor: not-allowed; }
.hero { padding: 64px 0 40px; }
.hero h1 { font-size: clamp(32px, 5.4vw, 52px); line-height: 1.08; letter-spacing: -.025em; margin: 0 0 18px; max-width: 820px; }
.hero p.lede { font-size: clamp(18px, 2.2vw, 21px); color: var(--soft); max-width: 680px; margin: 0 0 26px; }
.hero .ctas { display: flex; gap: 12px; flex-wrap: wrap; }
.hero .note { color: var(--faint); font-size: 14.5px; margin-top: 14px; }
.kicker { display: inline-block; font-size: 13px; font-weight: 700; letter-spacing: .06em; text-transform: uppercase; color: var(--sky); background: var(--sky-2); padding: 5px 10px; border-radius: 999px; margin-bottom: 18px; }
section { padding: 36px 0; }
h2 { font-size: clamp(24px, 3.2vw, 32px); letter-spacing: -.02em; line-height: 1.2; margin: 0 0 14px; }
.grid { display: grid; gap: 16px; grid-template-columns: repeat(auto-fit, minmax(240px, 1fr)); }
.card { background: var(--paper); border: 1px solid var(--line); border-radius: var(--radius); padding: 20px 22px; box-shadow: var(--shadow); }
.card h3 { margin: 0 0 6px; font-size: 18px; }
.card p { margin: 0; color: var(--soft); font-size: 15.5px; }
.facts { display: grid; grid-template-columns: repeat(auto-fit, minmax(150px, 1fr)); gap: 12px; }
.fact { background: var(--paper); border: 1px solid var(--line); border-radius: 12px; padding: 16px; }
.fact b { display: block; font-size: 26px; letter-spacing: -.02em; }
.fact span { color: var(--soft); font-size: 14.5px; }
table.compare { width: 100%; border-collapse: collapse; background: var(--paper); border: 1px solid var(--line); border-radius: var(--radius); overflow: hidden; font-size: 15.5px; }
table.compare th, table.compare td { text-align: left; padding: 12px 14px; border-bottom: 1px solid var(--line); vertical-align: top; }
table.compare th { background: var(--sky-2); }
.price { display: flex; flex-wrap: wrap; gap: 16px; align-items: stretch; }
.price .card { flex: 1 1 280px; }
.price .amount { font-size: 40px; font-weight: 800; letter-spacing: -.02em; }
.price ul { padding-left: 20px; margin: 10px 0 18px; color: var(--soft); }
details { background: var(--paper); border: 1px solid var(--line); border-radius: 12px; padding: 14px 18px; margin-bottom: 10px; }
details summary { cursor: pointer; font-weight: 700; }
details p { color: var(--soft); margin: 10px 0 0; }
footer { border-top: 1px solid var(--line); padding: 28px 0 40px; color: var(--faint); font-size: 14px; margin-top: 30px; }
footer a { color: var(--soft); }
.fine { color: var(--faint); font-size: 14px; }
/* articles */
article { padding: 36px 0; }
article h1 { font-size: clamp(30px, 4.6vw, 42px); line-height: 1.12; letter-spacing: -.02em; margin: 0 0 12px; }
article h2 { margin-top: 34px; font-size: 25px; }
article .meta { color: var(--faint); font-size: 14.5px; margin-bottom: 22px; }
article table { border-collapse: collapse; width: 100%; font-size: 15.5px; margin: 12px 0; }
article th, article td { border-bottom: 1px solid var(--line); padding: 9px 10px; text-align: left; }
.callout { background: var(--sky-2); border-radius: 12px; padding: 16px 18px; margin: 22px 0; }
.callout .btn { margin-top: 10px; }
.sources { font-size: 14.5px; color: var(--soft); }
/* practice app */
.app { padding-top: 26px; padding-bottom: 40px; }
.bar { display: flex; align-items: center; justify-content: space-between; gap: 12px; flex-wrap: wrap; margin-bottom: 14px; }
.progress { height: 8px; background: var(--line); border-radius: 99px; overflow: hidden; margin: 6px 0 18px; }
.progress i { display: block; height: 100%; background: var(--sky); width: 0; transition: width .25s ease; }
.qcard { background: var(--paper); border: 1px solid var(--line); border-radius: var(--radius); padding: 22px; box-shadow: var(--shadow); }
.qtopic { font-size: 13px; font-weight: 700; text-transform: uppercase; letter-spacing: .05em; color: var(--sky); }
.qtext { font-size: 20px; line-height: 1.45; margin: 8px 0 18px; font-weight: 650; }
.choice { display: flex; gap: 12px; align-items: flex-start; width: 100%; text-align: left; background: var(--bg); border: 1.5px solid var(--line); border-radius: 12px;
  padding: 14px 16px; margin-bottom: 10px; font: inherit; color: var(--ink); cursor: pointer; }
.choice:hover:not([disabled]) { border-color: var(--sky); }
.choice .letter { flex: 0 0 28px; height: 28px; border-radius: 50%; display: grid; place-items: center; background: var(--paper); border: 1.5px solid var(--line); font-weight: 700; font-size: 14px; }
.choice.right { border-color: var(--go); background: var(--go-2); }
.choice.wrong { border-color: var(--no); background: var(--no-2); }
.choice.picked { border-color: var(--sky); background: var(--sky-2); }
.explain { border-left: 4px solid var(--go); background: var(--go-2); padding: 12px 16px; border-radius: 0 12px 12px 0; margin-top: 8px; }
.explain.bad { border-color: var(--no); background: var(--no-2); }
.explain .src { display: block; margin-top: 8px; font-size: 14px; color: var(--soft); }
.row { display: flex; gap: 10px; flex-wrap: wrap; align-items: center; margin-top: 14px; }
.timer { font-variant-numeric: tabular-nums; font-weight: 700; }
.topiclist { display: grid; gap: 10px; grid-template-columns: repeat(auto-fit, minmax(230px, 1fr)); }
.topic { display: flex; justify-content: space-between; align-items: center; gap: 10px; }
.lock { font-size: 13px; color: var(--faint); }
.score { font-size: 44px; font-weight: 800; letter-spacing: -.02em; }
.pill { white-space: nowrap; display: inline-block; padding: 3px 10px; border-radius: 99px; font-size: 13px; font-weight: 700; }
.pill.ok { background: var(--go-2); color: var(--go); }
.pill.bad { background: var(--no-2); color: var(--no); }
.field { width: 100%; max-width: 360px; padding: 12px 14px; border-radius: 10px; border: 1.5px solid var(--line); background: var(--paper); color: var(--ink); font: inherit; }
.hidden { display: none !important; }
:focus-visible { outline: 3px solid var(--sun); outline-offset: 2px; }
.fig { margin: 0 0 16px; }
.fig img { display: block; width: 100%; max-height: 520px; object-fit: contain; background: #fff; border: 1px solid var(--line); border-radius: 10px; }
.fig figcaption { font-size: 13px; color: var(--faint); margin-top: 6px; }