:root {
  --bg: #ffffff;
  --fg: #1a1a1a;
  --muted: #6b7280;
  --label: #374151;
  --border: #e5e7eb;
  --border-strong: #d1d5db;
  --accent: #2563eb;
  --accent-hover: #1d4ed8;
  --accent-soft: rgba(37, 99, 235, 0.1);
  --code-bg: #f6f8fa;
  --card-bg: #fafafa;
  --danger: #dc2626;
  --success: #16a34a;
  --warn: #d97706;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0f1115;
    --fg: #e5e7eb;
    --muted: #9ca3af;
    --label: #d1d5db;
    --border: #27272a;
    --border-strong: #3f3f46;
    --accent: #60a5fa;
    --accent-hover: #93c5fd;
    --accent-soft: rgba(96, 165, 250, 0.15);
    --code-bg: #1a1d23;
    --card-bg: #16181d;
    --danger: #f87171;
    --success: #4ade80;
    --warn: #fbbf24;
  }
}

* { box-sizing: border-box; }

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  background: var(--bg);
  color: var(--fg);
  margin: 0;
  padding: 2rem 1rem;
  line-height: 1.5;
}

.container {
  max-width: 1080px;
  margin: 0 auto;
}

header {
  margin-bottom: 2rem;
}

header h1 {
  margin: 0 0 0.25rem;
  font-size: 1.75rem;
}

header p {
  margin: 0;
  color: var(--muted);
  max-width: 64ch;
}

.back-link {
  display: inline-block;
  color: var(--accent);
  text-decoration: none;
  margin-bottom: 1rem;
  font-size: 0.9rem;
}

.back-link:hover { text-decoration: underline; }

.tools-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(240px, 1fr));
  gap: 1rem;
}

.tool-card {
  display: block;
  padding: 1rem 1.25rem;
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  text-decoration: none;
  color: var(--fg);
  transition: border-color 0.15s, transform 0.15s;
}

.tool-card:hover {
  border-color: var(--accent);
  transform: translateY(-1px);
}

.tool-card h3 {
  margin: 0 0 0.25rem;
  font-size: 1rem;
}

.tool-card p {
  margin: 0;
  font-size: 0.85rem;
  color: var(--muted);
}

.tool-card .badge {
  display: inline-block;
  font-size: 0.7rem;
  padding: 1px 6px;
  border-radius: 10px;
  background: var(--accent-soft);
  color: var(--accent);
  margin-left: 0.4rem;
  vertical-align: middle;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.04em;
}

textarea, input[type="text"], input[type="number"], select {
  width: 100%;
  padding: 0.6rem 0.75rem;
  font-family: ui-monospace, "SF Mono", Menlo, Consolas, monospace;
  font-size: 0.9rem;
  background: var(--code-bg);
  color: var(--fg);
  border: 1px solid var(--border);
  border-radius: 6px;
  resize: vertical;
}

textarea { min-height: 240px; }

textarea:focus, input:focus, select:focus {
  outline: none;
  border-color: var(--accent);
}

label {
  display: block;
  font-size: 0.85rem;
  color: var(--label);
  margin-bottom: 0.35rem;
  margin-top: 1rem;
  font-weight: 500;
}

label:first-of-type { margin-top: 0; }

button {
  padding: 0.55rem 1rem;
  background: var(--accent);
  color: white;
  border: none;
  border-radius: 6px;
  font-size: 0.9rem;
  cursor: pointer;
  font-family: inherit;
}

button:hover { background: var(--accent-hover); }

button:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

button.secondary {
  background: transparent;
  color: var(--fg);
  border: 1px solid var(--border-strong);
}

button.secondary:hover {
  background: var(--card-bg);
  border-color: var(--accent);
}

button.chip {
  padding: 0.3rem 0.7rem;
  font-size: 0.8rem;
  border-radius: 16px;
  background: transparent;
  color: var(--label);
  border: 1px solid var(--border-strong);
}

button.chip:hover {
  border-color: var(--accent);
  color: var(--accent);
}

button.chip.active {
  background: var(--accent-soft);
  border-color: var(--accent);
  color: var(--accent);
  font-weight: 600;
}

.button-row {
  display: flex;
  gap: 0.5rem;
  margin: 1rem 0;
  flex-wrap: wrap;
}

.chip-row {
  display: flex;
  gap: 0.4rem;
  flex-wrap: wrap;
  margin-top: 0.4rem;
}

.two-col {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1rem;
}

.split {
  display: grid;
  grid-template-columns: minmax(260px, 320px) 1fr;
  gap: 1.5rem;
}

@media (max-width: 760px) {
  .two-col, .split { grid-template-columns: 1fr; }
}

.status {
  margin-top: 0.5rem;
  font-size: 0.85rem;
  min-height: 1.2em;
}

.status.error { color: var(--danger); }
.status.success { color: var(--success); }
.status.warn { color: var(--warn); }

.preview {
  padding: 1rem;
  background: var(--code-bg);
  border: 1px solid var(--border);
  border-radius: 6px;
  min-height: 160px;
  overflow: auto;
}

.preview pre {
  margin: 0;
  white-space: pre-wrap;
  word-break: break-word;
  font-family: ui-monospace, "SF Mono", Menlo, Consolas, monospace;
  font-size: 0.9rem;
}

.stats {
  display: flex;
  gap: 1.25rem;
  flex-wrap: wrap;
  font-size: 0.8rem;
  color: var(--muted);
  margin-top: 0.75rem;
  font-family: ui-monospace, "SF Mono", Menlo, Consolas, monospace;
}

.stats .dot {
  display: inline-block;
  width: 7px;
  height: 7px;
  border-radius: 50%;
  background: var(--muted);
  margin-right: 0.4rem;
  vertical-align: middle;
}

.stats .good { color: var(--success); }
.stats .good .dot { background: var(--success); }
.stats .neutral .dot { background: var(--accent); }

.result-display {
  padding: 1.5rem 1.25rem;
  background: var(--code-bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 1rem;
  flex-wrap: wrap;
}

.result-display .equation {
  font-family: ui-monospace, monospace;
  font-size: 0.85rem;
  color: var(--muted);
  margin-bottom: 0.35rem;
}

.result-display .value {
  font-family: ui-monospace, monospace;
  font-size: 2.5rem;
  font-weight: 700;
  color: var(--accent);
  line-height: 1;
}

.conversion-table {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(150px, 1fr));
  gap: 4px;
  margin-top: 0.75rem;
}

.conversion-table .row {
  display: flex;
  justify-content: space-between;
  padding: 6px 12px;
  font-family: ui-monospace, monospace;
  font-size: 0.85rem;
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: 6px;
  cursor: pointer;
  transition: border-color 0.15s, background 0.15s;
}

.conversion-table .row:hover {
  border-color: var(--border-strong);
}

.conversion-table .row.active {
  background: var(--accent-soft);
  border-color: var(--accent);
}

.conversion-table .row .px { color: var(--muted); }
.conversion-table .row .rem { color: var(--label); }
.conversion-table .row.active .rem { color: var(--accent); font-weight: 700; }

.section-head {
  font-size: 0.7rem;
  font-weight: 600;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--muted);
  margin: 1.25rem 0 0.5rem;
  padding-bottom: 0.4rem;
  border-bottom: 1px solid var(--border);
}

.section-head:first-child { margin-top: 0; }

input[type="range"] {
  width: 100%;
  accent-color: var(--accent);
}

footer {
  margin-top: 3rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--border);
  color: var(--muted);
  font-size: 0.85rem;
}

footer a { color: var(--accent); text-decoration: none; }
footer a:hover { text-decoration: underline; }