:root {
  --primary: #1e40af;
  --primary-dark: #1e3a8a;
  --primary-light: #dbeafe;
  --text: #1e293b;
  --text-muted: #64748b;
  --border: #e2e8f0;
  --bg: #f8fafc;
  --white: #ffffff;
  --radius: 8px;
}

* { box-sizing: border-box; margin: 0; padding: 0; }

body {
  font-family: system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  font-size: 16px;
  line-height: 1.6;
  color: var(--text);
  background: var(--bg);
}

/* ── Header ── */
header {
  background: var(--primary);
  color: white;
  padding: 0 1.5rem;
  position: sticky;
  top: 0;
  z-index: 10;
  box-shadow: 0 2px 8px rgba(0,0,0,0.15);
}
.header-inner {
  max-width: 960px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 58px;
  gap: 1rem;
}
.logo {
  font-size: 1.2rem;
  font-weight: 700;
  color: white;
  text-decoration: none;
  white-space: nowrap;
}
nav { display: flex; gap: 0.25rem; flex-wrap: wrap; }
nav a {
  color: rgba(255,255,255,0.85);
  text-decoration: none;
  font-size: 0.82rem;
  padding: 0.3rem 0.6rem;
  border-radius: 4px;
  transition: background 0.15s;
}
nav a:hover, nav a.active {
  background: rgba(255,255,255,0.18);
  color: white;
}

/* ── Layout ── */
main {
  max-width: 960px;
  margin: 0 auto;
  padding: 2rem 1.5rem 3rem;
}

/* ── Hero (homepage) ── */
.hero {
  text-align: center;
  padding: 2.5rem 0 2rem;
}
.hero h1 {
  font-size: 2.1rem;
  font-weight: 800;
  margin-bottom: 0.75rem;
  line-height: 1.25;
}
.hero p {
  color: var(--text-muted);
  font-size: 1.1rem;
  max-width: 580px;
  margin: 0 auto;
}

/* ── Tool cards grid ── */
.tools-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(270px, 1fr));
  gap: 1.25rem;
  margin-bottom: 2rem;
}
.tool-card {
  background: white;
  border: 1.5px solid var(--border);
  border-radius: var(--radius);
  padding: 1.5rem;
  text-decoration: none;
  color: var(--text);
  transition: box-shadow 0.15s, border-color 0.15s, transform 0.15s;
  display: block;
}
.tool-card:hover {
  box-shadow: 0 6px 20px rgba(30,64,175,0.1);
  border-color: var(--primary);
  transform: translateY(-2px);
}
.tool-card .icon { font-size: 2rem; margin-bottom: 0.75rem; }
.tool-card h2 { font-size: 1.1rem; font-weight: 700; margin-bottom: 0.4rem; }
.tool-card p { font-size: 0.875rem; color: var(--text-muted); line-height: 1.55; }

/* ── Calculator page header ── */
.calc-header { margin-bottom: 1.5rem; }
.breadcrumb {
  font-size: 0.82rem;
  color: var(--text-muted);
  margin-bottom: 0.5rem;
}
.breadcrumb a { color: var(--primary); text-decoration: none; }
.breadcrumb a:hover { text-decoration: underline; }
.calc-header h1 { font-size: 1.8rem; font-weight: 800; margin-bottom: 0.4rem; }
.calc-header > p { color: var(--text-muted); }

/* ── Calculator card ── */
.calc-card {
  background: white;
  border: 1.5px solid var(--border);
  border-radius: var(--radius);
  padding: 2rem;
  margin-bottom: 1.75rem;
}
.form-row {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1.25rem;
}
.form-group { margin-bottom: 1.25rem; }
.form-group:last-of-type { margin-bottom: 0; }
label {
  display: block;
  font-size: 0.875rem;
  font-weight: 600;
  margin-bottom: 0.375rem;
}
.hint { font-size: 0.775rem; color: var(--text-muted); margin-top: 0.25rem; }
input[type="number"],
input[type="date"],
select {
  width: 100%;
  padding: 0.625rem 0.875rem;
  border: 1.5px solid var(--border);
  border-radius: var(--radius);
  font-size: 1rem;
  color: var(--text);
  background: white;
  -webkit-appearance: none;
  appearance: none;
  transition: border-color 0.15s, box-shadow 0.15s;
}
input:focus, select:focus {
  outline: none;
  border-color: var(--primary);
  box-shadow: 0 0 0 3px var(--primary-light);
}
.calc-btn {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  background: var(--primary);
  color: white;
  font-size: 1rem;
  font-weight: 700;
  padding: 0.8rem 2rem;
  border: none;
  border-radius: var(--radius);
  cursor: pointer;
  width: 100%;
  margin-top: 1.5rem;
  transition: background 0.15s, transform 0.1s;
  letter-spacing: 0.01em;
}
.calc-btn:hover { background: var(--primary-dark); }
.calc-btn:active { transform: scale(0.99); }

/* ── Result ── */
.result-box {
  display: none;
  margin-top: 1.5rem;
  background: #eff6ff;
  border: 2px solid #93c5fd;
  border-radius: var(--radius);
  padding: 1.5rem;
  animation: fadeIn 0.2s ease;
}
.result-box.show { display: block; }
@keyframes fadeIn { from { opacity: 0; transform: translateY(6px); } to { opacity: 1; transform: none; } }
.result-label {
  font-size: 0.82rem;
  color: #1d4ed8;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 0.25rem;
}
.result-value {
  font-size: 2.25rem;
  font-weight: 800;
  color: var(--primary-dark);
  margin-bottom: 0.25rem;
}
.result-subtitle { font-size: 0.875rem; color: var(--text-muted); }
.breakdown {
  margin-top: 1rem;
  border-top: 1.5px solid #bfdbfe;
  padding-top: 1rem;
}
.breakdown-row {
  display: flex;
  justify-content: space-between;
  font-size: 0.875rem;
  padding: 0.3rem 0;
  border-bottom: 1px solid #e0effe;
}
.breakdown-row:last-child { border-bottom: none; }
.breakdown-row.total {
  font-weight: 700;
  font-size: 0.9375rem;
  border-top: 2px solid #93c5fd;
  margin-top: 0.25rem;
  padding-top: 0.5rem;
  border-bottom: none;
}
.result-note {
  font-size: 0.8rem;
  color: var(--text-muted);
  margin-top: 1rem;
  padding-top: 1rem;
  border-top: 1px solid #bfdbfe;
  line-height: 1.6;
}

/* ── AdSense placeholders ── */
.ad-slot {
  background: #f1f5f9;
  border: 1px dashed #94a3b8;
  border-radius: 4px;
  display: flex;
  align-items: center;
  justify-content: center;
  color: #94a3b8;
  font-size: 0.75rem;
  margin: 1.5rem 0;
  text-align: center;
}
.ad-728 { height: 90px; }
.ad-300 { height: 250px; max-width: 336px; }
.ad-320 { height: 50px; }

/* ── Info sections ── */
.info-section {
  background: white;
  border: 1.5px solid var(--border);
  border-radius: var(--radius);
  padding: 2rem;
  margin-bottom: 1.5rem;
}
.info-section h2 {
  font-size: 1.3rem;
  font-weight: 700;
  margin-bottom: 1rem;
  padding-bottom: 0.625rem;
  border-bottom: 2px solid var(--primary-light);
  color: var(--primary-dark);
}
.info-section h3 {
  font-size: 1rem;
  font-weight: 700;
  margin: 1.25rem 0 0.5rem;
  color: var(--text);
}
.info-section p { margin-bottom: 0.875rem; line-height: 1.75; }
.info-section ul { padding-left: 1.5rem; margin-bottom: 0.875rem; }
.info-section ul li { margin-bottom: 0.4rem; line-height: 1.65; }
.formula-box {
  background: var(--primary-light);
  border-left: 4px solid var(--primary);
  border-radius: 0 6px 6px 0;
  padding: 1rem 1.25rem;
  margin: 1rem 0;
  font-size: 1.05rem;
  font-weight: 600;
  text-align: center;
  color: var(--primary-dark);
}

/* ── FAQ ── */
.faq-item {
  border-bottom: 1px solid var(--border);
  padding: 1rem 0;
}
.faq-item:last-child { border-bottom: none; padding-bottom: 0; }
.faq-q {
  font-weight: 700;
  margin-bottom: 0.5rem;
  color: var(--text);
}
.faq-a { color: var(--text-muted); font-size: 0.9375rem; line-height: 1.7; }

/* ── Other tools nav ── */
.other-tools {
  background: white;
  border: 1.5px solid var(--border);
  border-radius: var(--radius);
  padding: 1.5rem;
  margin-top: 2rem;
}
.other-tools h3 {
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 1rem;
}
.other-tools-grid { display: flex; flex-wrap: wrap; gap: 0.625rem; }
.other-tools a {
  background: var(--bg);
  border: 1.5px solid var(--border);
  border-radius: 20px;
  padding: 0.4rem 1rem;
  font-size: 0.875rem;
  color: var(--primary);
  text-decoration: none;
  transition: background 0.15s, border-color 0.15s;
  font-weight: 500;
}
.other-tools a:hover {
  background: var(--primary-light);
  border-color: var(--primary);
}

/* ── Footer ── */
footer {
  background: #1e293b;
  color: #94a3b8;
  padding: 2rem 1.5rem;
  margin-top: 3rem;
  font-size: 0.875rem;
}
.footer-inner {
  max-width: 960px;
  margin: 0 auto;
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  align-items: center;
  gap: 0.75rem;
}
footer a { color: #94a3b8; text-decoration: none; transition: color 0.15s; }
footer a:hover { color: white; }
.footer-links { display: flex; gap: 1.25rem; flex-wrap: wrap; }

/* ── Mobile ── */
@media (max-width: 640px) {
  nav { display: none; }
  .hero h1 { font-size: 1.5rem; }
  .calc-header h1 { font-size: 1.4rem; }
  .calc-card { padding: 1.25rem; }
  .form-row { grid-template-columns: 1fr; }
  .result-value { font-size: 1.75rem; }
  .info-section { padding: 1.25rem; }
  .ad-728 { height: 50px; }
}