:root {
  --ink: #172523;
  --muted: #60706d;
  --paper: #fbfaf6;
  --surface: #ffffff;
  --line: #dbe2df;
  --green: #155f52;
  --green-dark: #0c493f;
  --mint: #dceee7;
  --red: #9e352a;
}

* { box-sizing: border-box; }
body {
  margin: 0;
  color: var(--ink);
  background:
    radial-gradient(circle at 8% 4%, rgba(220, 238, 231, .85), transparent 28rem),
    radial-gradient(circle at 94% 22%, rgba(240, 216, 170, .42), transparent 24rem),
    var(--paper);
  font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  line-height: 1.55;
}

main { min-height: 100vh; display: grid; place-items: center; padding: 28px; }
.card {
  width: min(100%, 680px);
  padding: clamp(28px, 6vw, 56px);
  background: rgba(255, 255, 255, .94);
  border: 1px solid var(--line);
  border-radius: 24px;
  box-shadow: 0 20px 60px rgba(23, 37, 35, .09);
}
.eyebrow { margin: 0 0 12px; color: var(--green); font-weight: 750; letter-spacing: .12em; text-transform: uppercase; font-size: 13px; }
h1 { margin: 0; font-family: Georgia, serif; font-size: clamp(32px, 6vw, 48px); line-height: 1.08; }
.intro { margin: 22px 0 32px; color: var(--muted); font-size: 17px; }
label { display: block; margin-bottom: 8px; font-weight: 700; }
.form-row { display: grid; grid-template-columns: 1fr auto; gap: 12px; }
input, button { min-height: 52px; border-radius: 12px; font: inherit; }
input { width: 100%; padding: 0 16px; border: 1px solid #aebbb7; font-size: 18px; letter-spacing: .07em; text-transform: uppercase; }
input:focus { outline: 3px solid rgba(21, 95, 82, .2); border-color: var(--green); }
button { padding: 0 24px; border: 0; background: var(--green); color: white; font-weight: 750; cursor: pointer; }
button:hover { background: var(--green-dark); }
button:disabled { opacity: .65; cursor: wait; }
.result { display: grid; gap: 3px; margin-top: 22px; padding: 17px 18px; border-radius: 12px; }
.result span { color: var(--muted); }
.result.valid { background: var(--mint); color: var(--green-dark); }
.result.invalid { background: #fff0ed; color: var(--red); }
.result.checking { background: #f1f3f2; color: var(--muted); }
.hidden { display: none; }

@media (max-width: 560px) {
  main { padding: 18px; }
  .form-row { grid-template-columns: 1fr; }
}