:root {
  --green: #2bb27b;
  --green-dark: #1f9465;
  --green-soft: #eefaf4;
  --ink: #1d2430;
  --muted: #5d6675;
  --line: #e2e6ec;
  --bg: #ffffff;
  --bg-soft: #f6f8fa;
  --red: #d64545;
  --red-soft: #fdf0f0;
  --radius: 14px;
  --shadow: 0 1px 2px rgba(16, 24, 40, .06), 0 6px 18px rgba(16, 24, 40, .06);
  --font: "Montserrat", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
}
* { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body { margin: 0; font-family: var(--font); color: var(--ink); background: var(--bg); line-height: 1.6; font-size: 17px; }
a { color: var(--green-dark); }
img { max-width: 100%; }
.wrap { max-width: 1080px; margin: 0 auto; padding: 0 20px; }
.narrow { max-width: 760px; margin: 0 auto; padding: 0 20px; }

/* header / footer */
.site-header { border-bottom: 1px solid var(--line); background: #fff; position: sticky; top: 0; z-index: 10; }
.site-header .wrap { display: flex; align-items: center; justify-content: space-between; height: 62px; gap: 16px; }
.logo { display: flex; align-items: center; gap: 8px; font-weight: 800; font-size: 20px; color: var(--ink); text-decoration: none; }
.logo-mark { width: 30px; height: 30px; border-radius: 8px; background: var(--green); color: #fff; display: grid; place-items: center; font-size: 15px; font-weight: 800; }
.nav { display: flex; gap: 18px; align-items: center; font-size: 15px; }
.nav a { color: var(--ink); text-decoration: none; font-weight: 600; }
.nav a:hover { color: var(--green-dark); }
.nav .btn { color: #fff; }
.site-footer { border-top: 1px solid var(--line); margin-top: 72px; padding: 36px 0; color: var(--muted); font-size: 14px; background: var(--bg-soft); }
.site-footer .cols { display: grid; grid-template-columns: repeat(auto-fit, minmax(200px, 1fr)); gap: 24px; }
.site-footer h4 { color: var(--ink); margin: 0 0 8px; font-size: 14px; }
.site-footer a { color: var(--muted); display: block; margin: 3px 0; text-decoration: none; }
.site-footer a:hover { color: var(--green-dark); }
.disclaimer { margin-top: 24px; font-size: 13px; }

/* buttons */
.btn { display: inline-block; background: var(--green); color: #fff; font-weight: 700; border: 0; border-radius: 999px; padding: 14px 28px; font-size: 17px; text-decoration: none; cursor: pointer; box-shadow: 0 3px 0 var(--green-dark); font-family: inherit; }
.btn:hover { background: var(--green-dark); }
.btn:disabled { opacity: .55; cursor: not-allowed; }
.btn-sm { padding: 9px 18px; font-size: 15px; box-shadow: 0 2px 0 var(--green-dark); }
.btn-ghost { background: #fff; color: var(--ink); border: 1px solid var(--line); box-shadow: none; }
.btn-ghost:hover { background: var(--bg-soft); }
.btn-block { display: block; width: 100%; text-align: center; }

/* hero */
.hero { padding: 64px 0 40px; text-align: center; }
.hero h1 { font-size: clamp(32px, 5vw, 50px); line-height: 1.15; margin: 0 auto 18px; max-width: 860px; letter-spacing: -.5px; }
.hero p.lead { font-size: 20px; color: var(--muted); max-width: 720px; margin: 0 auto 28px; }
.hero .sub { font-size: 14px; color: var(--muted); margin-top: 12px; }
.badges { display: flex; flex-wrap: wrap; gap: 10px; justify-content: center; margin-top: 30px; }
.badge { background: var(--bg-soft); border: 1px solid var(--line); border-radius: 999px; padding: 6px 14px; font-size: 14px; color: var(--muted); }

/* sections */
section { padding: 36px 0; }
section h2 { font-size: clamp(24px, 3.2vw, 32px); line-height: 1.25; margin: 0 0 14px; letter-spacing: -.3px; }
section h3 { font-size: 20px; margin: 22px 0 8px; }
.grid3 { display: grid; grid-template-columns: repeat(auto-fit, minmax(240px, 1fr)); gap: 18px; margin-top: 18px; }
.card { border: 1px solid var(--line); border-radius: var(--radius); padding: 22px; background: #fff; box-shadow: var(--shadow); }
.card h3 { margin-top: 0; }
.muted { color: var(--muted); }
.center { text-align: center; justify-content: center; }
.alt { background: var(--bg-soft); }
table.data { width: 100%; border-collapse: collapse; font-size: 15px; margin: 14px 0; }
table.data th, table.data td { border-bottom: 1px solid var(--line); padding: 10px 8px; text-align: left; vertical-align: top; }
table.data th { background: var(--bg-soft); font-weight: 700; }
.table-scroll { overflow-x: auto; }
.callout { border-left: 4px solid var(--green); background: var(--green-soft); padding: 14px 18px; border-radius: 8px; margin: 18px 0; }
.faq details { border-bottom: 1px solid var(--line); padding: 14px 0; }
.faq summary { font-weight: 700; cursor: pointer; }
.faq p { margin: 10px 0 0; color: var(--muted); }

/* pricing (mirrors the Excel Exercises grid) */
.pricing { max-width: 480px; margin: 0 auto; }
.pricing h2 { margin-bottom: 4px; }
.pricing .intro { color: var(--muted); margin: 0 0 18px; }
.plan { position: relative; display: flex; align-items: center; gap: 14px; border: 2px solid var(--line); border-radius: var(--radius); padding: 18px; margin-bottom: 14px; cursor: pointer; background: #fff; }
.plan input { position: absolute; opacity: 0; pointer-events: none; }
.plan .dot { width: 24px; height: 24px; border-radius: 50%; border: 2px solid #c8ced6; flex: none; display: grid; place-items: center; }
.plan.selected { border-color: var(--green); background: var(--green-soft); }
.plan.selected .dot { border-color: var(--green); background: var(--green); }
.plan.selected .dot::after { content: ""; width: 8px; height: 8px; background: #fff; border-radius: 50%; }
.plan .name { font-weight: 800; font-size: 18px; }
.plan .note { color: var(--muted); font-size: 15px; }
.plan .price { margin-left: auto; text-align: right; white-space: nowrap; }
.plan .price b { font-size: 26px; }
.plan .price span { color: var(--muted); font-size: 15px; }
.plan .tag { position: absolute; top: -13px; right: 18px; background: var(--green); color: #fff; font-size: 13px; font-weight: 700; border-radius: 999px; padding: 3px 12px; }
.pricing .fine { text-align: center; color: var(--muted); font-size: 14px; margin-top: 12px; line-height: 1.7; }

/* practice app */
.tabs { display: flex; gap: 8px; flex-wrap: wrap; margin: 22px 0; }
.tab { border: 1px solid var(--line); background: #fff; border-radius: 999px; padding: 9px 18px; font-weight: 700; cursor: pointer; font-family: inherit; font-size: 15px; color: var(--ink); }
.tab.active { background: var(--ink); color: #fff; border-color: var(--ink); }
.panel { display: none; }
.panel.active { display: block; }
.progress { height: 8px; background: var(--line); border-radius: 99px; overflow: hidden; margin: 6px 0 18px; }
.progress > i { display: block; height: 100%; background: var(--green); width: 0; transition: width .25s; }
.q-meta { font-size: 13px; color: var(--muted); text-transform: uppercase; letter-spacing: .4px; font-weight: 700; }
.q-stem { font-size: 21px; font-weight: 700; margin: 8px 0 16px; }
.opt { display: block; width: 100%; text-align: left; border: 2px solid var(--line); border-radius: 12px; background: #fff; padding: 14px 16px; margin-bottom: 10px; font-size: 17px; cursor: pointer; font-family: inherit; color: var(--ink); }
.opt:hover:not(:disabled) { border-color: #b9c2cd; }
.opt.correct { border-color: var(--green); background: var(--green-soft); }
.opt.wrong { border-color: var(--red); background: var(--red-soft); }
.opt:disabled { cursor: default; }
.explain { border-radius: 12px; background: var(--bg-soft); padding: 14px 16px; margin: 10px 0 16px; font-size: 16px; }
.explain .src { font-size: 13px; margin-top: 8px; color: var(--muted); }
.explain .src a { color: var(--muted); }
.row { display: flex; gap: 10px; align-items: center; flex-wrap: wrap; }
.calc-input { font-size: 20px; padding: 12px 14px; border: 2px solid var(--line); border-radius: 12px; width: 180px; font-family: inherit; }
.calc-input:focus, input[type=email]:focus { outline: none; border-color: var(--green); }
select { font-family: inherit; font-size: 15px; padding: 8px 10px; border-radius: 10px; border: 1px solid var(--line); background: #fff; }
.result-ok { color: var(--green-dark); font-weight: 700; }
.result-bad { color: var(--red); font-weight: 700; }
.steps { margin: 6px 0 0 18px; padding: 0; }
.flashcard { perspective: 1200px; height: 260px; margin: 10px 0 16px; cursor: pointer; }
.flashcard .inner { position: relative; width: 100%; height: 100%; transition: transform .45s; transform-style: preserve-3d; }
.flashcard.flipped .inner { transform: rotateY(180deg); }
.flashcard .face { position: absolute; inset: 0; backface-visibility: hidden; border: 2px solid var(--line); border-radius: var(--radius); background: #fff; display: flex; flex-direction: column; align-items: center; justify-content: center; padding: 18px; text-align: center; box-shadow: var(--shadow); }
.flashcard .back { transform: rotateY(180deg); background: var(--green-soft); border-color: var(--green); }
.flashcard .big { font-size: 34px; font-weight: 800; }
.flashcard .small { font-size: 15px; color: var(--muted); margin-top: 6px; }
.flashcard .back .small a { color: var(--muted); }
.pill { display: inline-block; font-size: 13px; font-weight: 700; padding: 2px 10px; border-radius: 99px; background: #fff; border: 1px solid var(--line); margin-top: 8px; }
.locked { border: 2px dashed #c8ced6; border-radius: var(--radius); padding: 18px; display: flex; gap: 12px; align-items: center; cursor: pointer; background: #fff; }
.locked:hover { border-color: var(--green); }
.paywall { scroll-margin-top: 80px; border: 2px solid var(--green); border-radius: var(--radius); padding: 26px 20px; margin: 22px 0; background: #fff; }
.paywall h2 { text-align: center; }
.paywall .intro { text-align: center; }
.score { font-size: 44px; font-weight: 800; text-align: center; }

/* reserve */
.form-card { max-width: 520px; margin: 0 auto; }
input[type=email] { width: 100%; font-size: 18px; padding: 14px; border: 2px solid var(--line); border-radius: 12px; font-family: inherit; margin: 8px 0 12px; }
.hp { position: absolute; left: -9999px; }
.ok-box { background: var(--green-soft); border: 1px solid var(--green); border-radius: 12px; padding: 16px; }

/* guides */
.article h1 { font-size: clamp(30px, 4.5vw, 42px); line-height: 1.2; margin: 44px 0 10px; letter-spacing: -.4px; }
.article .byline { color: var(--muted); font-size: 14px; margin-bottom: 22px; }
.article h2 { font-size: 26px; margin: 34px 0 10px; }
.article ul, .article ol { padding-left: 22px; }
.article li { margin: 4px 0; }
.sources { font-size: 14px; color: var(--muted); border-top: 1px solid var(--line); margin-top: 34px; padding-top: 16px; }
.sources a { color: var(--muted); word-break: break-word; }
.cta-box { border: 1px solid var(--line); border-radius: var(--radius); padding: 22px; margin: 28px 0; text-align: center; background: var(--bg-soft); }

@media (max-width: 640px) {
  body { font-size: 16px; }
  .nav a.hide-sm { display: none; }
  .hero { padding: 40px 0 24px; }
  .hero p.lead { font-size: 18px; }
  .plan { padding: 14px; gap: 10px; }
  .plan .price b { font-size: 22px; }
  .q-stem { font-size: 19px; }
  .flashcard .big { font-size: 28px; }
}

/* paid app */
.opt.chosen { border-color: var(--ink); background: var(--bg-soft); }
.timer { font-weight: 800; font-variant-numeric: tabular-nums; }
.exam-map { margin-top: 18px; }
.exam-nav { display: flex; flex-wrap: wrap; gap: 6px; margin-top: 10px; }
.qn { width: 40px; height: 34px; border-radius: 8px; border: 1px solid var(--line); background: #fff; cursor: pointer; font-family: inherit; font-weight: 600; }
.qn.done { background: var(--green-soft); border-color: var(--green); }
.qn.flag { box-shadow: inset 0 -3px 0 #e0a800; }
.qn.cur { outline: 2px solid var(--ink); }
.card.review { margin: 14px 0; }
#app .tabs { margin-top: 8px; }