/* Mobile-first: mặc định cho màn hình hẹp, mở rộng ở @media min-width */
:root {
  --bg: #f6f7f9;
  --card: #ffffff;
  --text: #16202c;
  --muted: #5b6878;
  --line: #e1e5ea;
  --brand: #0b7a5b;
  --brand-ink: #ffffff;
  --accent-bg: #e8f5f0;
  --radius: 12px;
  color-scheme: light dark;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0f1419;
    --card: #182029;
    --text: #e6ebf0;
    --muted: #9aa7b4;
    --line: #2a3542;
    --brand: #3ccf9e;
    --brand-ink: #062419;
    --accent-bg: #14342a;
  }
}
* { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font: 16px/1.55 system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
}
a { color: var(--brand); }
.wrap { max-width: 720px; margin: 0 auto; padding: 0 16px; }

header.site { background: var(--card); border-bottom: 1px solid var(--line); }
header.site .wrap { display: flex; align-items: center; justify-content: space-between; min-height: 56px; gap: 12px; }
.logo { font-weight: 700; font-size: 18px; color: var(--text); text-decoration: none; }
.logo span { color: var(--brand); }
nav.site { display: flex; gap: 14px; font-size: 14px; overflow-x: auto; }
nav.site a { text-decoration: none; white-space: nowrap; color: var(--muted); }
nav.site a[aria-current="page"] { color: var(--brand); font-weight: 600; }

main { padding: 20px 0 40px; }
h1 { font-size: 24px; line-height: 1.25; margin: 0 0 6px; }
h2 { font-size: 19px; margin: 28px 0 10px; }
.lead { color: var(--muted); margin: 0 0 18px; }

.card { background: var(--card); border: 1px solid var(--line); border-radius: var(--radius); padding: 16px; margin-bottom: 16px; }

.field { margin-bottom: 14px; }
.field label { display: block; font-weight: 600; font-size: 14px; margin-bottom: 6px; }
.field small { display: block; color: var(--muted); font-size: 13px; margin-top: 4px; }
input[type="text"], input[type="number"], select {
  width: 100%;
  min-height: 48px; /* đủ lớn để bấm trên điện thoại */
  padding: 10px 12px;
  font-size: 18px; /* ≥16px để iOS không tự phóng to */
  color: var(--text);
  background: var(--bg);
  border: 1px solid var(--line);
  border-radius: 10px;
}
input:focus, select:focus { outline: 2px solid var(--brand); outline-offset: 1px; }
.row { display: grid; grid-template-columns: 1fr 1fr; gap: 12px; }

.seg { display: grid; grid-auto-flow: column; grid-auto-columns: 1fr; border: 1px solid var(--line); border-radius: 10px; overflow: hidden; margin-bottom: 14px; }
.seg input { position: absolute; opacity: 0; pointer-events: none; }
.seg label { text-align: center; padding: 11px 6px; font-weight: 600; font-size: 15px; cursor: pointer; }
.seg label small { display: block; font-size: 12px; font-weight: 400; opacity: .85; }
.seg input:checked + label { background: var(--brand); color: var(--brand-ink); }
.seg input:focus-visible + label { outline: 2px solid var(--brand); outline-offset: -3px; }

.result { background: var(--accent-bg); border-color: transparent; }
.big { font-size: 30px; font-weight: 700; color: var(--brand); line-height: 1.2; font-variant-numeric: tabular-nums; }
.big-label { font-size: 14px; color: var(--muted); }

table { width: 100%; border-collapse: collapse; font-size: 15px; font-variant-numeric: tabular-nums; }
td, th { padding: 8px 4px; border-bottom: 1px solid var(--line); text-align: left; }
td.n, th.n { text-align: right; white-space: nowrap; }
tr.total td { font-weight: 700; border-bottom: 0; }
.scroll { overflow-x: auto; max-height: 420px; overflow-y: auto; }
.scroll table { font-size: 13px; min-width: 400px; }
.scroll th { position: sticky; top: 0; background: var(--card); }

.tools { display: grid; gap: 12px; }
.tools a { display: block; text-decoration: none; color: var(--text); }
.tools a strong { color: var(--brand); display: block; font-size: 17px; }
.tools a span { color: var(--muted); font-size: 14px; }

.note { font-size: 13px; color: var(--muted); }
footer.site { border-top: 1px solid var(--line); padding: 20px 0 32px; font-size: 13px; color: var(--muted); }

@media (min-width: 640px) {
  h1 { font-size: 30px; }
  .tools { grid-template-columns: 1fr 1fr; }
  .big { font-size: 36px; }
}