:root {
  --bg: #f7f8fa;
  --surface: #ffffff;
  --text: #1a1d21;
  --text-muted: #5c6470;
  --border: #e4e7ec;
  --primary: #2563eb;
  --primary-hover: #1d4ed8;
  --primary-contrast: #ffffff;
  --chip-active: #2563eb;
  --shadow: 0 1px 3px rgba(16, 24, 40, 0.08), 0 8px 24px rgba(16, 24, 40, 0.06);
  --radius: 16px;
}

:root[data-theme="dark"] {
  --bg: #0f1115;
  --surface: #191c22;
  --text: #f2f4f7;
  --text-muted: #9aa4b2;
  --border: #2a2f3a;
  --primary: #3b82f6;
  --primary-hover: #60a5fa;
  --primary-contrast: #ffffff;
  --chip-active: #3b82f6;
  --shadow: 0 1px 3px rgba(0, 0, 0, 0.4), 0 8px 24px rgba(0, 0, 0, 0.35);
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #0f1115;
    --surface: #191c22;
    --text: #f2f4f7;
    --text-muted: #9aa4b2;
    --border: #2a2f3a;
    --primary: #3b82f6;
    --primary-hover: #60a5fa;
    --primary-contrast: #ffffff;
    --chip-active: #3b82f6;
    --shadow: 0 1px 3px rgba(0, 0, 0, 0.4), 0 8px 24px rgba(0, 0, 0, 0.35);
  }
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}

.site-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  max-width: 760px;
  margin: 0 auto;
  padding: 20px 24px;
}

.brand {
  font-weight: 700;
  font-size: 1.1rem;
}

.theme-toggle {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 999px;
  width: 40px;
  height: 40px;
  font-size: 1.1rem;
  cursor: pointer;
  color: var(--text);
}

main {
  max-width: 760px;
  margin: 0 auto;
  padding: 0 24px 64px;
}

.hero {
  text-align: center;
  padding: 24px 0 8px;
}

h1 {
  font-size: clamp(1.7rem, 5vw, 2.6rem);
  line-height: 1.15;
  margin: 8px 0 12px;
  letter-spacing: -0.02em;
}

.subtitle {
  color: var(--text-muted);
  font-size: 1.05rem;
  max-width: 520px;
  margin: 0 auto 32px;
}

.tool {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 36px 28px;
  margin: 0 auto;
  max-width: 520px;
}

.result {
  display: block;
  font-size: clamp(2rem, 8vw, 3rem);
  font-weight: 700;
  letter-spacing: 0.01em;
  font-variant-numeric: tabular-nums;
  padding: 8px 0 4px;
  word-break: break-word;
}

.results-list {
  display: flex;
  flex-direction: column;
  gap: 8px;
  margin: 8px 0 4px;
}

.results-list .num {
  font-size: 1.5rem;
  font-weight: 600;
  font-variant-numeric: tabular-nums;
  padding: 10px 12px;
  border-radius: 10px;
  background: var(--bg);
  border: 1px solid var(--border);
}

.actions {
  display: flex;
  gap: 12px;
  justify-content: center;
  margin: 24px 0 20px;
  flex-wrap: wrap;
}

.btn {
  font-size: 1rem;
  font-weight: 600;
  border-radius: 12px;
  padding: 14px 28px;
  cursor: pointer;
  border: 1px solid transparent;
  transition: transform 0.05s ease, background 0.15s ease;
}

.btn:active {
  transform: translateY(1px);
}

.btn-primary {
  background: var(--primary);
  color: var(--primary-contrast);
}

.btn-primary:hover {
  background: var(--primary-hover);
}

.btn-secondary {
  background: transparent;
  color: var(--text);
  border-color: var(--border);
}

.btn-secondary:hover {
  border-color: var(--primary);
  color: var(--primary);
}

.quantity {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 12px;
}

.quantity-label {
  color: var(--text-muted);
  font-size: 0.95rem;
}

.quantity-options {
  display: inline-flex;
  gap: 6px;
}

.chip {
  min-width: 44px;
  padding: 8px 14px;
  border-radius: 10px;
  border: 1px solid var(--border);
  background: transparent;
  color: var(--text);
  font-weight: 600;
  cursor: pointer;
}

.chip.is-active {
  background: var(--chip-active);
  color: #fff;
  border-color: var(--chip-active);
}

.copied-note {
  color: var(--primary);
  font-weight: 600;
  text-align: center;
  margin: 16px 0 0;
}

.content {
  margin-top: 56px;
}

.content h2 {
  font-size: 1.35rem;
  margin: 32px 0 10px;
  letter-spacing: -0.01em;
}

.content p,
.content li {
  color: var(--text-muted);
}

.content ul {
  padding-left: 20px;
}

.content li {
  margin: 6px 0;
}

.faq details {
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 4px 16px;
  margin: 10px 0;
  background: var(--surface);
}

.faq summary {
  cursor: pointer;
  font-weight: 600;
  color: var(--text);
  padding: 10px 0;
}

.faq details p {
  margin: 0 0 12px;
}

.site-footer {
  border-top: 1px solid var(--border);
  padding: 28px 24px;
  text-align: center;
}

.footer-links {
  display: flex;
  gap: 20px;
  justify-content: center;
  margin-bottom: 10px;
}

.footer-links a {
  color: var(--text-muted);
  text-decoration: none;
  font-size: 0.95rem;
}

.footer-links a:hover {
  color: var(--primary);
}

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