:root {
  --bg: #f5f7fb;
  --bg-elev: #ffffff;
  --text: #0f172a;
  --text-muted: #64748b;
  --border: #e2e8f0;
  --border-strong: #cbd5e1;
  --primary: #2563eb;
  --primary-soft: #dbeafe;
  --green: #10b981;
  --green-soft: #d1fae5;
  --purple: #8b5cf6;
  --purple-soft: #ede9fe;
  --danger: #ef4444;
  --shadow-sm: 0 1px 2px rgba(15, 23, 42, 0.05);
  --shadow-md: 0 6px 16px -4px rgba(15, 23, 42, 0.08), 0 2px 4px -1px rgba(15, 23, 42, 0.04);
  --radius: 14px;
  --radius-sm: 8px;
}

[data-theme="dark"] {
  --bg: #0b1220;
  --bg-elev: #131c2e;
  --text: #e2e8f0;
  --text-muted: #94a3b8;
  --border: #1f2a44;
  --border-strong: #2a3754;
  --primary: #60a5fa;
  --primary-soft: #1e3a8a;
  --green: #34d399;
  --green-soft: #064e3b;
  --purple: #a78bfa;
  --purple-soft: #4c1d95;
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.4);
  --shadow-md: 0 8px 24px -6px rgba(0, 0, 0, 0.5), 0 2px 6px -1px rgba(0, 0, 0, 0.3);
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
  transition: background-color 0.2s ease, color 0.2s ease;
}

/* Top bar */
.topbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 18px 32px;
  background: var(--bg-elev);
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 10;
  backdrop-filter: blur(8px);
}

.brand {
  display: flex;
  align-items: center;
  gap: 14px;
}

.logo {
  width: 44px;
  height: 44px;
  border-radius: 12px;
  background: linear-gradient(135deg, var(--primary), var(--purple));
  color: white;
  display: grid;
  place-items: center;
  font-weight: 800;
  font-size: 16px;
  letter-spacing: 0.5px;
  box-shadow: var(--shadow-md);
}

.brand h1 {
  margin: 0;
  font-size: 20px;
  font-weight: 700;
  letter-spacing: -0.01em;
}

.tag {
  margin: 0;
  font-size: 12px;
  color: var(--text-muted);
  font-weight: 500;
}

.theme-toggle {
  background: transparent;
  border: 1px solid var(--border);
  border-radius: 10px;
  width: 40px;
  height: 40px;
  display: grid;
  place-items: center;
  cursor: pointer;
  color: var(--text);
  transition: all 0.15s ease;
}

.theme-toggle:hover { border-color: var(--border-strong); background: var(--bg); }

.theme-toggle svg { width: 18px; height: 18px; }
[data-theme="dark"] .icon-sun { display: none; }
:root:not([data-theme="dark"]) .icon-moon { display: none; }

/* Container */
.container {
  max-width: 1100px;
  margin: 0 auto;
  padding: 32px;
  display: flex;
  flex-direction: column;
  gap: 24px;
}

/* Cards */
.card {
  background: var(--bg-elev);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow-sm);
  overflow: hidden;
  transition: box-shadow 0.2s ease, transform 0.2s ease;
}

.card:hover { box-shadow: var(--shadow-md); }

.card-head {
  display: flex;
  align-items: flex-start;
  gap: 16px;
  padding: 22px 24px 16px;
  border-bottom: 1px solid var(--border);
}

.card-head h2 {
  margin: 0 0 4px;
  font-size: 18px;
  font-weight: 700;
  letter-spacing: -0.01em;
}

.muted { color: var(--text-muted); margin: 0; font-size: 13px; }

.badge {
  font-size: 11px;
  font-weight: 700;
  padding: 6px 10px;
  border-radius: 999px;
  letter-spacing: 0.5px;
  flex-shrink: 0;
}

.badge-blue { background: var(--primary-soft); color: var(--primary); }
.badge-green { background: var(--green-soft); color: var(--green); }
.badge-purple { background: var(--purple-soft); color: var(--purple); }

.card-body { padding: 24px; }

.grid-2 {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 24px;
  align-items: stretch;
}

/* Form fields */
.field { display: flex; flex-direction: column; gap: 6px; }
.field-wide { margin-bottom: 20px; }

label {
  font-size: 13px;
  font-weight: 600;
  color: var(--text);
}

.input-prefix {
  display: flex;
  align-items: center;
  background: var(--bg);
  border: 1.5px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 0 12px;
  transition: border-color 0.15s ease, box-shadow 0.15s ease;
}

.input-prefix:focus-within {
  border-color: var(--primary);
  box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.15);
}

.prefix {
  font-weight: 600;
  color: var(--text-muted);
  font-size: 14px;
  padding-right: 8px;
  border-right: 1px solid var(--border);
  margin-right: 8px;
}

.input-prefix input {
  flex: 1;
  border: none;
  outline: none;
  background: transparent;
  font-size: 16px;
  font-weight: 600;
  color: var(--text);
  padding: 12px 0;
  font-family: inherit;
  width: 100%;
}

.input-prefix input::placeholder { color: var(--text-muted); font-weight: 400; }

.hint { font-size: 12px; color: var(--text-muted); margin: 0; }

select {
  border: 1.5px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 12px 14px;
  font-family: inherit;
  font-size: 14px;
  font-weight: 600;
  background: var(--bg);
  color: var(--text);
  cursor: pointer;
  outline: none;
  transition: border-color 0.15s ease;
}

select:focus { border-color: var(--primary); }

/* Result block */
.result {
  background: linear-gradient(135deg, var(--primary-soft), transparent);
  border: 1px dashed var(--primary);
  border-radius: var(--radius-sm);
  padding: 20px;
  display: flex;
  flex-direction: column;
  justify-content: center;
  gap: 12px;
}

.result-label {
  font-size: 12px;
  font-weight: 700;
  letter-spacing: 0.5px;
  text-transform: uppercase;
  color: var(--primary);
}

.result-value {
  font-size: 32px;
  font-weight: 800;
  letter-spacing: -0.02em;
  color: var(--text);
  font-variant-numeric: tabular-nums;
}

.result-breakdown {
  display: flex;
  flex-direction: column;
  gap: 4px;
  font-size: 13px;
  color: var(--text-muted);
  padding-top: 8px;
  border-top: 1px solid rgba(37, 99, 235, 0.2);
}

.result-breakdown strong {
  color: var(--text);
  font-weight: 600;
  font-variant-numeric: tabular-nums;
  margin-left: 8px;
}

.result-breakdown span {
  display: flex;
  justify-content: space-between;
}

/* Periods */
.periods {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 14px;
}

.period {
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 18px;
  text-align: center;
  transition: transform 0.15s ease, border-color 0.15s ease;
}

.period:hover {
  transform: translateY(-2px);
  border-color: var(--green);
}

.period-label {
  font-size: 12px;
  font-weight: 700;
  letter-spacing: 0.5px;
  text-transform: uppercase;
  color: var(--text-muted);
  margin-bottom: 8px;
}

.period-value {
  font-size: 24px;
  font-weight: 800;
  letter-spacing: -0.02em;
  font-variant-numeric: tabular-nums;
  color: var(--text);
  margin-bottom: 6px;
}

.period-formula {
  font-size: 11px;
  color: var(--text-muted);
  font-family: 'SF Mono', Menlo, Consolas, monospace;
}

/* Rule finder */
.rule-finder {
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 18px;
  margin-bottom: 20px;
}

.rule-controls {
  display: flex;
  gap: 10px;
  align-items: stretch;
}

.flex-1 { flex: 1; }

.rule-result {
  margin-top: 14px;
  padding: 12px 14px;
  background: var(--bg-elev);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  font-size: 14px;
  min-height: 42px;
  display: flex;
  align-items: center;
  gap: 8px;
}

.rule-result.match {
  border-color: var(--purple);
  background: var(--purple-soft);
}

.rule-result strong {
  color: var(--purple);
  font-variant-numeric: tabular-nums;
}

[data-theme="dark"] .rule-result.match { background: rgba(139, 92, 246, 0.15); }
[data-theme="dark"] .rule-result.match strong { color: var(--purple); }

/* Tiers table */
.table-wrap {
  overflow-x: auto;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
}

.tiers {
  width: 100%;
  border-collapse: collapse;
  font-size: 14px;
}

.tiers th {
  background: var(--bg);
  color: var(--text-muted);
  font-size: 12px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.5px;
  text-align: left;
  padding: 12px 16px;
  border-bottom: 1px solid var(--border);
}

.tiers td {
  padding: 14px 16px;
  border-bottom: 1px solid var(--border);
  font-variant-numeric: tabular-nums;
  font-weight: 600;
}

.tiers tbody tr { transition: background 0.15s ease; }
.tiers tbody tr:hover { background: var(--bg); }

.tiers tbody tr.highlight {
  background: var(--purple-soft);
}

[data-theme="dark"] .tiers tbody tr.highlight { background: rgba(139, 92, 246, 0.2); }

.tiers tbody tr.highlight td { color: var(--purple); }
[data-theme="dark"] .tiers tbody tr.highlight td { color: #c4b5fd; }

.tiers tfoot td {
  background: var(--bg);
  color: var(--text-muted);
  font-size: 13px;
  font-weight: 500;
  border-bottom: none;
  font-variant-numeric: normal;
}

/* Footer */
.footer {
  margin-top: 16px;
  text-align: center;
  color: var(--text-muted);
  font-size: 12px;
}
.footer p { margin: 0; }

/* Responsive */
@media (max-width: 720px) {
  .topbar { padding: 14px 18px; }
  .brand h1 { font-size: 17px; }
  .container { padding: 18px; gap: 18px; }
  .card-body { padding: 18px; }
  .card-head { padding: 18px 18px 14px; }
  .grid-2 { grid-template-columns: 1fr; gap: 18px; }
  .periods { grid-template-columns: 1fr; }
  .result-value { font-size: 28px; }
  .rule-controls { flex-direction: column; }
  select { width: 100%; }
}