:root {
  --blue: #1557d6;
  --blue-dark: #0c3fa1;
  --blue-pale: #eaf1ff;
  --ink: #172033;
  --muted: #65708a;
  --line: #dce3ef;
  --surface: #ffffff;
  --canvas: #f7f9fd;
  font-family: "Noto Sans KR", system-ui, sans-serif;
  color: var(--ink);
  background: var(--canvas);
}

* { box-sizing: border-box; }

body {
  margin: 0;
  min-width: 320px;
  background:
    radial-gradient(circle at 85% 5%, #dfeaff 0, transparent 22rem),
    var(--canvas);
}

button, input { font: inherit; }

.page-shell { width: min(100% - 40px, 760px); margin: 0 auto; padding: 88px 0 56px; }

.hero { margin-bottom: 34px; }

.eyebrow {
  display: flex;
  align-items: center;
  gap: 8px;
  margin: 0 0 12px;
  color: var(--blue);
  font: 500 12px/1 "DM Mono", monospace;
  letter-spacing: .08em;
}

.eyebrow span { display: inline-block; width: 8px; height: 8px; background: var(--blue); border-radius: 50%; }

h1, h2, p { margin-top: 0; }
h1 { margin-bottom: 12px; font-size: clamp(38px, 7vw, 58px); line-height: 1.16; letter-spacing: -.06em; }
h2 { margin-bottom: 8px; font-size: 20px; letter-spacing: -.04em; }
.intro { margin-bottom: 0; color: var(--muted); font-size: 17px; line-height: 1.75; }

.checker-card { padding: 32px; border: 1px solid var(--line); border-radius: 18px; background: var(--surface); box-shadow: 0 14px 40px rgba(20, 48, 96, .07); }
label { display: block; margin-bottom: 10px; font-weight: 700; }
.input-row { display: flex; gap: 10px; }

input {
  min-width: 0;
  flex: 1;
  padding: 14px 16px;
  border: 1px solid #bac6da;
  border-radius: 10px;
  outline: none;
  color: var(--ink);
  background: #fff;
  font: 500 18px "DM Mono", monospace;
}
input:focus { border-color: var(--blue); box-shadow: 0 0 0 4px rgba(21, 87, 214, .12); }

#check-button {
  padding: 14px 19px;
  border: 0;
  border-radius: 10px;
  color: white;
  background: var(--blue);
  font-weight: 700;
  cursor: pointer;
  transition: background .18s, transform .18s;
}
#check-button:hover { background: var(--blue-dark); transform: translateY(-1px); }

.input-help { margin: 10px 0 24px; color: var(--muted); font-size: 13px; }
.result { display: flex; align-items: center; gap: 14px; min-height: 90px; padding: 17px; border-radius: 12px; background: var(--blue-pale); }
.result-icon { display: grid; width: 48px; height: 48px; flex: 0 0 48px; place-items: center; border-radius: 50%; color: var(--blue); background: #fff; font: 500 22px "DM Mono", monospace; }
.result-label { margin-bottom: 4px; color: var(--blue); font: 500 11px/1 "DM Mono", monospace; letter-spacing: .08em; }
.result-message { margin-bottom: 0; font-size: 15px; font-weight: 600; line-height: 1.55; }
.result-detail { margin: 7px 0 0; color: var(--muted); font-size: 13px; line-height: 1.6; }
.result--prime .result-detail { color: #357457; }
.result--not-prime .result-detail { color: #9d5149; }
.result--error .result-detail { color: #846c2e; }
.result--prime { background: #e8f7ef; }
.result--prime .result-icon, .result--prime .result-label { color: #147446; }
.result--not-prime { background: #fff0ee; }
.result--not-prime .result-icon, .result--not-prime .result-label { color: #c33b2c; }
.result--error { background: #fff7df; }
.result--error .result-icon, .result--error .result-label { color: #9a6900; }

.info-grid { display: grid; grid-template-columns: repeat(2, 1fr); gap: 14px; margin: 14px 0 58px; }
.info-grid article { padding: 21px; border: 1px solid var(--line); border-radius: 14px; background: rgba(255, 255, 255, .65); }
.card-number { margin-bottom: 28px; color: var(--blue); font: 500 12px "DM Mono", monospace; }
.info-grid h2 { font-size: 17px; }
.info-grid article p:last-child { margin-bottom: 0; color: var(--muted); font-size: 14px; line-height: 1.7; }

.section-heading { display: flex; align-items: end; justify-content: space-between; gap: 16px; margin-bottom: 16px; }
.section-heading .eyebrow { margin-bottom: 9px; }
.section-heading h2 { margin: 0; }
.text-button { padding: 4px 0; border: 0; color: var(--blue); background: transparent; font-size: 13px; font-weight: 700; cursor: pointer; }
.text-button:disabled { color: #aeb8c8; cursor: default; }
.history-list { display: grid; gap: 9px; padding: 0; margin: 0; list-style: none; }
.history-list li { display: flex; align-items: center; justify-content: space-between; padding: 15px 17px; border: 1px solid var(--line); border-radius: 10px; background: #fff; }
.history-number { font: 500 16px "DM Mono", monospace; }
.history-badge { padding: 5px 9px; border-radius: 999px; font-size: 12px; font-weight: 700; }
.history-badge--prime { color: #147446; background: #e8f7ef; }
.history-badge--not-prime { color: #c33b2c; background: #fff0ee; }
.history-empty { justify-content: center !important; min-height: 60px; color: var(--muted); font-size: 14px; }
footer { padding: 26px 20px 36px; border-top: 1px solid var(--line); color: var(--muted); text-align: center; font-size: 12px; }

@media (max-width: 520px) {
  .page-shell { width: min(100% - 28px, 760px); padding-top: 54px; }
  .checker-card { padding: 22px; }
  .input-row { flex-direction: column; }
  #check-button { width: 100%; }
  .info-grid { grid-template-columns: 1fr; margin-bottom: 44px; }
}