:root {
  color-scheme: light dark;
  --bg: #f4f5f7;
  --card: #ffffff;
  --text: #15181e;
  --muted: #586070;
  --border: #e1e4ea;
  --accent: #2f4fcf;
  --ok: #12703f;
  --ok-bg: #e7f5ed;
  --bad: #b42323;
  --bad-bg: #fcecec;
  --warn: #8f5200;
  --warn-bg: #fff3dc;
  --pending: #8a919e;
  --mark: #ffe08a;
  --mark-text: #15181e;
  --sans: system-ui, -apple-system, "Segoe UI", Roboto, "Noto Sans", "Helvetica Neue", Arial, sans-serif;
  --mono: ui-monospace, "SF Mono", SFMono-Regular, Menlo, Consolas, "Liberation Mono", monospace;
  --radius: 14px;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0e1014;
    --card: #171a20;
    --text: #e7e9ee;
    --muted: #9ba3b2;
    --border: #2a2f39;
    --accent: #93a7ff;
    --ok: #63d398;
    --ok-bg: #11271b;
    --bad: #ff8a8a;
    --bad-bg: #2d1517;
    --warn: #ffc266;
    --warn-bg: #2b2111;
    --pending: #6c7482;
    --mark: #6b5310;
    --mark-text: #fff6d8;
  }
}

*, *::before, *::after { box-sizing: border-box; }
[hidden] { display: none !important; }

html { -webkit-text-size-adjust: 100%; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font: 16px/1.55 var(--sans);
}

a { color: var(--accent); text-underline-offset: 2px; }
a:hover { text-decoration-thickness: 2px; }

.wrap {
  max-width: 760px;
  margin: 0 auto;
  padding: 40px 20px 56px;
}

.sr-only {
  position: absolute;
  width: 1px; height: 1px;
  padding: 0; margin: -1px;
  overflow: hidden; clip: rect(0 0 0 0);
  white-space: nowrap; border: 0;
}

.muted { color: var(--muted); }

/* --- Header --------------------------------------------------------------- */

.masthead h1 {
  margin: 0 0 8px;
  font-size: clamp(1.8rem, 4vw, 2.4rem);
  line-height: 1.15;
  letter-spacing: -0.02em;
}

.tagline {
  margin: 0 0 20px;
  color: var(--muted);
}

/* --- Cards ------------------------------------------------------------------ */

.card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 24px;
  margin-bottom: 20px;
}

/* --- Input ------------------------------------------------------------------ */

.field-label {
  display: block;
  font-weight: 600;
  margin-bottom: 8px;
}

.field { position: relative; }

#number {
  width: 100%;
  padding: 14px 92px 14px 16px;
  font: 600 clamp(1.35rem, 5vw, 1.9rem)/1.2 var(--mono);
  font-variant-numeric: tabular-nums;
  letter-spacing: 0.06em;
  color: var(--text);
  background: var(--bg);
  border: 2px solid var(--border);
  border-radius: 12px;
  outline: none;
  transition: border-color 0.15s, box-shadow 0.15s;
}

#number::placeholder { color: var(--pending); opacity: 0.6; }

#number:focus {
  border-color: var(--accent);
  box-shadow: 0 0 0 4px color-mix(in srgb, var(--accent) 18%, transparent);
}

.clear {
  position: absolute;
  right: 10px;
  top: 50%;
  transform: translateY(-50%);
  padding: 7px 12px;
  font: 500 0.9rem var(--sans);
  color: var(--muted);
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 8px;
  cursor: pointer;
}

.clear:hover { color: var(--text); }
.clear:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }

/* --- Status banner ------------------------------------------------------------ */

.status {
  display: flex;
  gap: 12px;
  align-items: flex-start;
  margin-top: 16px;
  padding: 14px 16px;
  border-radius: 12px;
  background: var(--bg);
  border: 1px solid var(--border);
}

.status p { margin: 0; }
.status-title { font-weight: 650; font-size: 1.08rem; }
.status-detail { color: var(--muted); margin-top: 2px !important; font-size: 0.95rem; }
.status-detail:empty { display: none; }

.status-icon {
  flex: none;
  display: grid;
  place-items: center;
  width: 28px; height: 28px;
  border-radius: 50%;
  font-weight: 800;
  font-size: 0.95rem;
  color: #fff;
  background: var(--pending);
}

.status-icon::before { content: "?"; }

.state-incomplete .status-icon::before { content: "\2026"; }

.state-valid { background: var(--ok-bg); border-color: color-mix(in srgb, var(--ok) 35%, transparent); }
.state-valid .status-title { color: var(--ok); }
.state-valid .status-icon { background: var(--ok); color: var(--card); }
.state-valid .status-icon::before { content: "\2713"; }

.state-invalid { background: var(--bad-bg); border-color: color-mix(in srgb, var(--bad) 35%, transparent); }
.state-invalid .status-title { color: var(--bad); }
.state-invalid .status-icon { background: var(--bad); color: var(--card); }
.state-invalid .status-icon::before { content: "\2715"; }

.state-too-long { background: var(--warn-bg); border-color: color-mix(in srgb, var(--warn) 35%, transparent); }
.state-too-long .status-title { color: var(--warn); }
.state-too-long .status-icon { background: var(--warn); color: var(--card); }
.state-too-long .status-icon::before { content: "!"; }

/* --- Rule checklist --------------------------------------------------------------- */

.rules {
  list-style: none;
  margin: 16px 0 0;
  padding: 0;
  display: grid;
  gap: 2px;
}

.rule {
  display: flex;
  gap: 10px;
  align-items: flex-start;
  padding: 7px 4px;
}

.rule-icon {
  flex: none;
  width: 20px; height: 20px;
  margin-top: 2px;
  border-radius: 50%;
  display: grid;
  place-items: center;
  font-size: 0.72rem;
  font-weight: 800;
  border: 2px solid var(--pending);
  color: var(--pending);
}

.rule.pass .rule-icon { background: var(--ok); border-color: var(--ok); color: var(--card); }
.rule.pass .rule-icon::before { content: "\2713"; }
.rule.fail .rule-icon { background: var(--bad); border-color: var(--bad); color: var(--card); }
.rule.fail .rule-icon::before { content: "\2715"; }
.rule.pending .rule-icon { border-style: dashed; }

.rule-text strong { font-weight: 600; margin-right: 6px; }
.rule.pending .rule-text strong { color: var(--muted); }
.rule-detail { color: var(--muted); font-size: 0.94rem; }

/* --- Suggestions ------------------------------------------------------------------- */

.suggestions {
  margin-top: 20px;
  padding-top: 18px;
  border-top: 1px solid var(--border);
}

.suggestions h2 { font-size: 1.1rem; margin: 0 0 2px; }
.suggestions h3 { font-size: 0.95rem; margin: 14px 0 6px; }
.suggestions p { margin: 0 0 8px; font-size: 0.95rem; }

.cands {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  gap: 6px;
}

.cands li {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  justify-content: space-between;
  gap: 4px 14px;
  padding: 8px 12px;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: var(--bg);
}

.num {
  font: 600 1.12rem var(--mono);
  font-variant-numeric: tabular-nums;
  letter-spacing: 0.05em;
  white-space: pre;
}

.num mark {
  background: var(--mark);
  color: var(--mark-text);
  border-radius: 3px;
  padding: 0 1px;
}

.cand-note { color: var(--muted); font-size: 0.86rem; }

.cand-side {
  display: inline-flex;
  align-items: center;
  gap: 12px;
  margin-left: auto;
}

.cands .num { user-select: all; }

.copy {
  min-width: 72px;
  padding: 4px 10px;
  font: 500 0.84rem var(--sans);
  color: var(--accent);
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 7px;
  cursor: pointer;
  transition: border-color 0.15s, color 0.15s;
}

.copy:hover { border-color: var(--accent); }
.copy:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
.copy.copied { color: var(--ok); border-color: var(--ok); }
.copy.copy-failed { color: var(--bad); border-color: var(--bad); }

.copy-buffer {
  position: fixed;
  top: 0; left: 0;
  width: 1px; height: 1px;
  opacity: 0;
  pointer-events: none;
}

details.subs { margin-top: 14px; }

details > summary {
  cursor: pointer;
  font-weight: 600;
  padding: 4px 0;
}

details > summary:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; border-radius: 4px; }
details[open] > summary { margin-bottom: 6px; }

/* --- Checksum steps ------------------------------------------------------------------ */

.steps {
  margin-top: 20px;
  padding-top: 14px;
  border-top: 1px solid var(--border);
}


.table-scroll { overflow-x: auto; }

table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.92rem;
  font-variant-numeric: tabular-nums;
}

th, td {
  text-align: left;
  padding: 6px 10px;
  border-bottom: 1px solid var(--border);
  white-space: nowrap;
}

th { font-weight: 600; color: var(--muted); font-size: 0.84rem; }
td { font-family: var(--mono); }
tr.check-row td { background: color-mix(in srgb, var(--accent) 8%, transparent); }

.steps-result { font-weight: 600; margin: 12px 0 0; }
.steps-result .ok { color: var(--ok); }
.steps-result .bad { color: var(--bad); }

/* --- Footer ------------------------------------------------------------------------ */

.foot {
  color: var(--muted);
  font-size: 0.88rem;
  text-align: center;
  margin-top: 28px;
}

@media (max-width: 520px) {
  .wrap { padding: 24px 14px 40px; }
  .card { padding: 18px 16px; }
  #number { padding-right: 80px; letter-spacing: 0.03em; }
}

@media (prefers-reduced-motion: reduce) {
  * { transition: none !important; }
}