/* Shared styles for Bytesize CS practice tools.
   Same palette as the splash page and GCSE site: Tailwind slate neutrals, blue accent. */
:root {
  --bg: #f8fafc; --card: #ffffff; --ink: #0f172a; --muted: #475569; --line: #e2e8f0;
  --blue: #2563eb; --blue-dark: #1d4ed8; --blue-soft: #eff6ff; --blue-line: #bfdbfe;
  --good: #15803d; --good-soft: #f0fdf4; --good-line: #bbf7d0;
  --bad: #b91c1c; --bad-soft: #fef2f2; --bad-line: #fecaca;
  --neg: #7c3aed; --neg-soft: #f5f3ff; --neg-line: #ddd6fe;
  --font: ui-sans-serif, system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --mono: ui-monospace, "Cascadia Mono", Consolas, "SF Mono", Menlo, monospace;
}
* { box-sizing: border-box; }
[hidden] { display: none !important; }
body { margin: 0; background: var(--bg); color: var(--ink); font-family: var(--font); line-height: 1.55; }
.wrap { max-width: 860px; margin: 0 auto; padding-inline: 16px; }
@media (min-width: 640px) { .wrap { padding-inline: 24px; } }

header.bar { background: var(--card); border-bottom: 1px solid var(--line); }
header.bar .wrap { display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: 8px 16px; padding-block: 12px; }
.brand { display: flex; align-items: center; gap: 10px; text-decoration: none; color: inherit; }
.brand b { font-size: 19px; }
.byte { display: grid; grid-template-columns: repeat(4, 7px); gap: 2px; }
.byte i { width: 7px; height: 7px; border-radius: 2px; background: var(--blue-line); }
.byte i.on { background: var(--blue); }
.navlinks { display: flex; gap: 14px; font-size: 14px; }
.navlinks a { color: var(--blue-dark); text-decoration: none; font-weight: 600; }
.navlinks a:hover { text-decoration: underline; }

main { padding-block: 28px 48px; display: grid; gap: 18px; }
h1 { margin: 0; font-size: clamp(26px, 4vw, 34px); letter-spacing: -0.02em; }
.intro { margin: 4px 0 0; color: var(--muted); }

.card { background: var(--card); border: 1px solid var(--line); border-radius: 16px; padding: 22px; box-shadow: 0 1px 2px rgba(15, 23, 42, .05); }

.levels { display: flex; flex-wrap: wrap; gap: 6px; }
.levels button { font: 600 14px var(--font); padding: 7px 12px; border-radius: 999px; border: 1px solid var(--line); background: var(--card); color: var(--muted); cursor: pointer; }
.levels button[aria-pressed="true"] { background: var(--blue); border-color: var(--blue); color: #fff; }
.levels button .lv { font-weight: 400; opacity: .8; }
.opts { display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: 10px; margin-top: 14px; }
.toggle { display: flex; align-items: center; gap: 8px; font-size: 15px; cursor: pointer; }
.toggle input { width: 18px; height: 18px; accent-color: var(--blue); }

.stats { display: flex; gap: 18px; font-size: 14px; color: var(--muted); }
.stats b { color: var(--ink); font-variant-numeric: tabular-nums; font-size: 16px; }

/* the number */
.question { margin-top: 18px; overflow-x: auto; padding-bottom: 4px; }
.grid { display: grid; grid-template-columns: repeat(var(--n), minmax(40px, 64px)); gap: 6px; justify-content: center; }
.pv { text-align: center; font: 600 14px var(--mono); color: var(--muted); padding: 4px 0; border-radius: 6px; font-variant-numeric: tabular-nums; }
.pv.neg { color: var(--neg); }
.pv.hit { background: var(--blue-soft); color: var(--blue-dark); }
.pv.hit.neg { background: var(--neg-soft); color: var(--neg); }
.places-off .pv { visibility: hidden; }
.bit { display: grid; place-items: center; aspect-ratio: 4 / 5; font: 700 clamp(22px, 4vw, 32px) var(--mono); border-radius: 10px; border: 2px solid var(--line); background: var(--card); color: var(--muted); }
.bit.one { background: var(--blue); border-color: var(--blue); color: #fff; }
.bit.one.neg { background: var(--neg); border-color: var(--neg); }
.caption { text-align: center; margin: 10px 0 0; font-size: 14px; color: var(--muted); }

form.answer { display: flex; flex-wrap: wrap; justify-content: center; align-items: center; gap: 10px; margin-top: 20px; }
form.answer label { font-weight: 600; }
form.answer input { width: 9ch; font: 700 24px var(--mono); text-align: center; padding: 8px 10px; border-radius: 10px; border: 2px solid var(--line); color: var(--ink); background: var(--card); }
form.answer input:focus { outline: none; border-color: var(--blue); box-shadow: 0 0 0 3px var(--blue-line); }
.btn { font: 600 16px var(--font); padding: 10px 18px; border-radius: 10px; border: 1px solid var(--blue); background: var(--blue); color: #fff; cursor: pointer; }
.btn:hover { background: var(--blue-dark); }
.btn.secondary { background: var(--card); color: var(--blue-dark); border-color: var(--blue-line); }
.btn.secondary:hover { background: var(--blue-soft); }
.btn:focus-visible, .levels button:focus-visible, .navlinks a:focus-visible { outline: 3px solid var(--blue); outline-offset: 2px; }

.feedback { margin-top: 16px; border-radius: 12px; padding: 14px 16px; border: 1px solid; display: grid; gap: 4px; }
.feedback.good { background: var(--good-soft); border-color: var(--good-line); }
.feedback.bad { background: var(--bad-soft); border-color: var(--bad-line); }
.feedback strong { font-size: 17px; }
.feedback.good strong { color: var(--good); }
.feedback.bad strong { color: var(--bad); }
.feedback .working { font: 600 16px var(--mono); overflow-wrap: anywhere; }
.feedback .row { display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: 10px; margin-top: 6px; }
.feedback .hint { font-size: 14px; color: var(--muted); }

details.how { background: var(--card); border: 1px solid var(--line); border-radius: 16px; padding: 4px 22px; }
details.how summary { cursor: pointer; font-weight: 700; padding-block: 12px; }
details.how p, details.how ol { margin: 0 0 12px; max-width: 68ch; }
details.how code { font-family: var(--mono); background: var(--bg); border: 1px solid var(--line); border-radius: 4px; padding: 0 4px; }
footer { color: var(--muted); font-size: 13px; text-align: center; }
@media (prefers-reduced-motion: no-preference) {
  .bit { transition: background .15s, border-color .15s; }
  .pop { animation: pop .25s ease-out; }
  @keyframes pop { from { transform: scale(.97); opacity: .4; } to { transform: none; opacity: 1; } }
}

/* Clickable bit tiles (denary to binary) */
button.bit { font: 700 clamp(22px, 4vw, 32px) var(--mono); padding: 0; cursor: pointer; width: 100%; }
button.bit:hover:not(:disabled) { border-color: var(--blue); }
button.bit:focus-visible { outline: 3px solid var(--blue); outline-offset: 2px; }
button.bit:disabled { cursor: default; }
.bit.wrong { border-color: var(--bad); box-shadow: 0 0 0 3px var(--bad-line); }
.bit.small { aspect-ratio: auto; padding-block: 6px; font-size: 20px; border-width: 1px; }
.target { text-align: center; margin: 0; }
.target span { display: block; font-size: 14px; color: var(--muted); }
.target b { font: 700 clamp(40px, 8vw, 56px) var(--mono); letter-spacing: -0.02em; font-variant-numeric: tabular-nums; }
.target b.neg { color: var(--neg); }
.actions { display: flex; flex-wrap: wrap; justify-content: center; align-items: center; gap: 10px; margin-top: 18px; }
.running { text-align: center; margin: 10px 0 0; font-size: 14px; color: var(--muted); font-variant-numeric: tabular-nums; }
.running b { color: var(--ink); font-family: var(--mono); }
.correct-row { margin-top: 8px; display: grid; gap: 6px; }
.correct-row .label { font-size: 14px; color: var(--muted); }
.steps { margin: 0; padding-left: 20px; font: 600 15px var(--mono); }

/* Phones: let the card shrink, and size the eight tiles to fit a 375px screen */
main > * { min-width: 0; }
@media (max-width: 480px) {
  .card { padding: 16px; }
  .grid { grid-template-columns: repeat(var(--n), minmax(0, 1fr)); gap: 4px; }
  .pv { font-size: 12px; }
  .bit, button.bit { border-radius: 8px; font-size: 22px; }
  .stats { gap: 12px; }
}

/* Column addition (binary addition) */
.sum { display: grid; grid-template-columns: minmax(26px, max-content) repeat(var(--n), minmax(0, 52px)) minmax(3.2em, auto); gap: 6px; justify-content: center; align-items: center; }
.sum .lbl { text-align: center; font: 700 22px var(--mono); color: var(--muted); }
.sum .lbl.small { font: 600 12px var(--font); }
.sum .digit { text-align: center; font: 700 clamp(20px, 3.6vw, 30px) var(--mono); padding-block: 4px; }
.sum .den { font: 600 14px var(--mono); color: var(--muted); padding-left: 6px; white-space: nowrap; }
.sum .rule { grid-column: 1 / -1; border-top: 2px solid var(--ink); margin-block: 2px; }
.sum .pv.ovf { color: var(--bad); opacity: .7; }
button.carry { font: 700 15px var(--mono); height: 30px; border-radius: 8px; border: 1px dashed var(--line); background: transparent; color: var(--neg); cursor: pointer; padding: 0; width: 100%; }
button.carry:hover:not(:disabled) { border-color: var(--neg); }
button.carry:focus-visible { outline: 3px solid var(--blue); outline-offset: 1px; }
button.carry:disabled { cursor: default; }
.carry.shown { border-style: solid; border-color: var(--neg-line); background: var(--neg-soft); }
.bit.ovf { border-style: dashed; }
.bit.ovf.one { border-style: solid; }
.ovf-label { text-align: center; font: 600 11px var(--font); color: var(--bad); text-transform: uppercase; letter-spacing: .04em; }
.hide-den .den { visibility: hidden; }
@media (max-width: 480px) {
  .sum { grid-template-columns: minmax(16px, max-content) repeat(var(--n), minmax(0, 1fr)) minmax(2.6em, auto); gap: 3px; }
  .sum .lbl { font-size: 18px; }
  .sum .lbl.small { font-size: 10px; }
  .sum .digit { font-size: 18px; }
  .sum .den { font-size: 12px; padding-left: 2px; }
  button.carry { height: 26px; font-size: 13px; }
  .sum .bit, .sum button.bit { font-size: 18px; border-width: 1.5px; border-radius: 6px; }
}
.carry-note { font: 500 11px var(--font); color: var(--neg); line-height: 1.2; padding-left: 4px; }

/* Hexadecimal: nibble groups, hex digit boxes, reference table */
.levels + .levels { margin-top: 8px; }
.levels.modes button { border-radius: 10px; }
.nibbles { display: flex; justify-content: center; gap: 18px; }
.nib { display: grid; gap: 6px; flex: 0 1 260px; min-width: 0; }
.nib .grid { grid-template-columns: repeat(4, minmax(0, 1fr)); justify-content: stretch; }
.nib-label { text-align: center; font: 700 15px var(--mono); color: var(--blue-dark); background: var(--blue-soft); border: 1px solid var(--blue-line); border-radius: 8px; padding: 2px 0; }
.nib-label.empty { visibility: hidden; }
.hexbox { display: flex; justify-content: center; gap: 8px; }
.hexbox .col { display: grid; gap: 6px; justify-items: center; }
.hexbox .digit-tile { display: grid; place-items: center; width: clamp(56px, 12vw, 76px); aspect-ratio: 4 / 5; font: 700 clamp(30px, 6vw, 42px) var(--mono); border-radius: 12px; border: 2px solid var(--blue-line); background: var(--blue-soft); color: var(--blue-dark); }
.hexbox .pv { min-width: 4ch; }
.err-inline { text-align: center; margin: 8px 0 0; color: var(--bad); font-size: 14px; }
form.answer input.hex { text-transform: uppercase; }
table.hex-table { border-collapse: collapse; font: 500 14px var(--mono); margin-bottom: 14px; }
table.hex-table th, table.hex-table td { border: 1px solid var(--line); padding: 3px 9px; text-align: center; }
table.hex-table th { font-family: var(--font); font-weight: 700; background: var(--bg); }
table.hex-table td.h { font-weight: 700; color: var(--blue-dark); }
.table-scroll { overflow-x: auto; }
@media (max-width: 480px) {
  .nibbles { gap: 10px; }
}

/* Two-step conversions (going via binary) */
.stepper { display: flex; justify-content: center; align-items: center; flex-wrap: wrap; gap: 6px; margin-top: 16px; font-size: 14px; }
.stepper .chip { padding: 3px 12px; border-radius: 999px; border: 1px solid var(--line); color: var(--muted); font-weight: 600; }
.stepper .chip.now { background: var(--blue); border-color: var(--blue); color: #fff; }
.stepper .chip.done { background: var(--blue-soft); border-color: var(--blue-line); color: var(--blue-dark); }
.stepper .arrow { color: var(--muted); }
.stepper .stepno { width: 100%; text-align: center; color: var(--muted); font-size: 13px; }
.steps li.head { list-style: none; margin-left: -20px; font-family: var(--font); font-weight: 700; margin-top: 6px; }
.steps li.head:first-child { margin-top: 0; }
.steps li.head .ok { color: var(--good); } .steps li.head .no { color: var(--bad); }