:root {
  --bg: #f4f6f9;
  --surface: #ffffff;
  --border: #e2e8f0;
  --text: #0f172a;
  --text-muted: #64748b;
  --primary: #1d4ed8;
  --success: #15803d;
  --success-soft: #f0fdf4;
  --success-border: #bbf7d0;
  --warning: #b45309;
  --warning-soft: #fffbeb;
  --warning-border: #fde68a;
  --danger: #b91c1c;
  --danger-soft: #fef2f2;
  --danger-border: #fecaca;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  background: var(--bg);
  color: var(--text);
  padding: 1rem;
  -webkit-font-smoothing: antialiased;
}

.container {
  width: 100%;
  max-width: 520px;
}

.card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 14px;
  box-shadow: 0 4px 16px rgba(15, 23, 42, 0.06);
  padding: 1.75rem;
}

h1 {
  margin: 0 0 0.35rem;
  font-size: 1.5rem;
  font-weight: 700;
  letter-spacing: -0.02em;
}

.subtitle {
  margin: 0 0 1.4rem;
  font-size: 0.85rem;
  color: var(--text-muted);
}

label {
  display: block;
  font-size: 0.9rem;
  font-weight: 600;
  margin-bottom: 0.45rem;
}

.input-row {
  display: flex;
  gap: 0.5rem;
  align-items: center;
}

input[type="text"] {
  flex: 1;
  font-family: inherit;
  font-size: 1.05rem;
  padding: 0.7rem 0.9rem;
  border: 1px solid #cbd5e1;
  border-radius: 9px;
  color: var(--text);
  background: var(--surface);
  min-width: 0;
}

input[type="text"]:focus {
  outline: 2px solid var(--primary);
  outline-offset: 1px;
  border-color: var(--primary);
}

.btn-clear {
  font-family: inherit;
  font-size: 0.88rem;
  font-weight: 600;
  padding: 0.65rem 0.9rem;
  border: 1px solid var(--border);
  border-radius: 9px;
  background: var(--surface);
  color: var(--text-muted);
  cursor: pointer;
  flex-shrink: 0;
}

.btn-clear:hover {
  color: var(--text);
  background: #f8fafc;
}

.hidden {
  display: none !important;
}

.result-area {
  margin-top: 1.25rem;
}

.result-box {
  border-radius: 10px;
  padding: 1.1rem 1.2rem;
  border: 1px solid;
}

.result-box.success {
  background: var(--success-soft);
  border-color: var(--success-border);
}

.result-box.warning {
  background: var(--warning-soft);
  border-color: var(--warning-border);
}

.result-box.error {
  background: var(--danger-soft);
  border-color: var(--danger-border);
}

.result-top {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  gap: 0.75rem;
}

.result-label {
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  color: var(--success);
  margin-bottom: 0.2rem;
}

.result-box.warning .result-label {
  color: var(--warning);
}

.result-box.error .result-label {
  color: var(--danger);
}

.result-date {
  margin: 0;
  font-size: 1.35rem;
  font-weight: 700;
  color: var(--text);
}

.result-meta {
  margin: 0.45rem 0 0;
  font-size: 0.86rem;
  color: var(--text-muted);
}

.btn-copy {
  font-family: inherit;
  font-size: 0.82rem;
  font-weight: 600;
  padding: 0.4rem 0.75rem;
  background: #ffffff;
  color: var(--success);
  border: 1px solid var(--success-border);
  border-radius: 7px;
  cursor: pointer;
  white-space: nowrap;
}

.btn-copy:hover {
  background: var(--success-soft);
}

.year-warning {
  margin-top: 0.75rem;
  padding: 0.65rem 0.9rem;
  border-radius: 8px;
  background: var(--warning-soft);
  border: 1px solid var(--warning-border);
  color: var(--warning);
  font-size: 0.86rem;
  font-weight: 600;
}