:root {
  --bg: #f5f7fa;
  --card: #ffffff;
  --fg: #16202b;
  --muted: #5b6470;
  --line: #d9dee5;
  --accent: #1f5fa8;
  --accent-fg: #ffffff;
  --error: #b42318;
  --ok: #1b7f3b;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #0f1318; --card: #171c22; --fg: #e8eaed; --muted: #9aa3ad; --line: #2b323a;
    --accent: #6ea8ff; --accent-fg: #0b1220; --error: #f87171; --ok: #4ade80;
  }
}
* { box-sizing: border-box; }
body {
  margin: 0; min-height: 100vh; display: grid; place-items: center;
  background: var(--bg); color: var(--fg);
  font: 16px/1.5 system-ui, -apple-system, "Segoe UI", Roboto, Arial, sans-serif;
  padding: 16px;
}
main { width: 100%; max-width: 420px; }
.card { background: var(--card); border: 1px solid var(--line); border-radius: 12px; padding: 28px 24px; }
h1 { font-size: 1.35rem; margin: 0 0 4px; }
.sub { color: var(--muted); margin: 0 0 20px; font-size: .95rem; }
label { display: block; font-weight: 600; margin: 0 0 6px; font-size: .9rem; }
input {
  width: 100%; padding: 11px 12px; font: inherit; color: var(--fg); background: transparent;
  border: 1px solid var(--line); border-radius: 8px;
}
input:focus { outline: 2px solid var(--accent); outline-offset: 1px; }
input.code { letter-spacing: .4em; font-size: 1.3rem; text-align: center; font-variant-numeric: tabular-nums; }
button {
  width: 100%; margin-top: 16px; padding: 11px 12px; font: inherit; font-weight: 600;
  background: var(--accent); color: var(--accent-fg); border: 0; border-radius: 8px; cursor: pointer;
}
button[disabled] { opacity: .6; cursor: default; }
.link { background: none; color: var(--accent); width: auto; padding: 0; margin-top: 14px; font-weight: 500; }
.msg { margin-top: 14px; font-size: .92rem; min-height: 1.2em; }
.msg.error { color: var(--error); }
.msg.ok { color: var(--ok); }
.help { color: var(--muted); font-size: .85rem; margin-top: 20px; border-top: 1px solid var(--line); padding-top: 14px; }
.demo { margin-top: 12px; padding: 8px 10px; border: 1px dashed var(--muted); border-radius: 8px; font-size: .85rem; }
[hidden] { display: none !important; }