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

:root {
  --bg-primary: #f8f9fc;
  --bg-card: #ffffff;
  --bg-hero: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
  --text-primary: #1a1d2e;
  --text-secondary: #5f6785;
  --text-muted: #9498b0;
  --border: #e8eaf2;
  --shadow-sm: 0 1px 3px rgba(0,0,0,.06), 0 1px 2px rgba(0,0,0,.04);
  --shadow-md: 0 4px 12px rgba(0,0,0,.07), 0 2px 4px rgba(0,0,0,.04);
  --radius: 12px;
  --radius-lg: 16px;
  --transition: .25s cubic-bezier(.4,0,.2,1);
  --accent: #667eea;
  --accent-light: #eef0ff;
}

html { scroll-behavior: smooth; }

body {
  font-family: 'Inter', 'Noto Sans SC', -apple-system, BlinkMacSystemFont, sans-serif;
  background: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}

a { text-decoration: none; color: inherit; }

.tool-header {
  background: var(--bg-card);
  border-bottom: 1px solid var(--border);
  padding: 0 24px;
  height: 64px;
  display: flex; align-items: center; gap: 16px;
  position: sticky; top: 0; z-index: 100;
  backdrop-filter: blur(20px);
}

.back-btn {
  display: inline-flex; align-items: center; gap: 6px;
  padding: 8px 16px; border-radius: 8px;
  font-size: 14px; font-weight: 500;
  color: var(--text-secondary);
  background: var(--bg-primary);
  border: 1px solid var(--border);
  cursor: pointer; transition: var(--transition);
}

.back-btn:hover { border-color: var(--accent); color: var(--accent); }

.tool-header-title {
  font-size: 18px; font-weight: 600;
  display: flex; align-items: center; gap: 10px;
}

.tool-body {
  max-width: 960px;
  margin: 32px auto;
  padding: 0 24px;
}

.tool-card-main {
  background: var(--bg-card);
  border-radius: var(--radius-lg);
  border: 1px solid var(--border);
  padding: 32px;
  box-shadow: var(--shadow-sm);
}

.tool-card-main h2 {
  font-size: 13px; font-weight: 600; text-transform: uppercase;
  color: var(--accent); letter-spacing: 0.05em;
  margin-bottom: 20px;
}

label {
  display: block; font-size: 14px; font-weight: 500;
  color: var(--text-secondary); margin-bottom: 6px;
}

input[type="text"], input[type="number"], input[type="date"],
textarea, select {
  width: 100%; padding: 10px 14px;
  border: 1.5px solid var(--border); border-radius: 8px;
  font-size: 15px; font-family: inherit;
  background: var(--bg-primary);
  outline: none; transition: var(--transition);
  color: var(--text-primary);
}

input:focus, textarea:focus, select:focus {
  border-color: var(--accent);
  box-shadow: 0 0 0 3px rgba(102,126,234,.15);
}

textarea { resize: vertical; min-height: 120px; }

.btn {
  display: inline-flex; align-items: center; justify-content: center; gap: 6px;
  padding: 10px 24px; border: none; border-radius: 8px;
  font-size: 15px; font-weight: 600; font-family: inherit;
  cursor: pointer; transition: var(--transition);
}

.btn-primary {
  background: var(--bg-hero); color: #fff;
  box-shadow: 0 2px 8px rgba(102,126,234,.35);
}

.btn-primary:hover { opacity: .9; transform: translateY(-1px); }

.btn-secondary {
  background: var(--bg-primary); color: var(--text-secondary);
  border: 1.5px solid var(--border);
}

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

.result-box {
  margin-top: 20px; padding: 20px;
  background: var(--accent-light);
  border-radius: var(--radius);
  border: 1px solid rgba(102,126,234,.2);
}

.result-box .result-label {
  font-size: 13px; font-weight: 600; color: var(--accent);
  margin-bottom: 8px;
}

.result-box .result-value {
  font-size: 24px; font-weight: 700; color: var(--text-primary);
  word-break: break-all;
}

.result-box .result-detail {
  font-size: 14px; color: var(--text-secondary);
  margin-top: 8px;
}

.form-row {
  display: flex; gap: 16px; margin-bottom: 16px;
}

.form-row > * { flex: 1; }

.form-group { margin-bottom: 16px; }

.btn-row {
  display: flex; gap: 12px; margin-top: 20px;
}

.unsupported-box {
  text-align: center; padding: 80px 20px;
}

.unsupported-box .icon { font-size: 64px; margin-bottom: 20px; }

.unsupported-box h2 {
  font-size: 22px; font-weight: 600; color: var(--text-primary);
  margin-bottom: 12px;
}

.unsupported-box p {
  font-size: 15px; color: var(--text-muted); max-width: 400px;
  margin: 0 auto;
}

.copy-btn {
  background: none; border: 1px solid var(--border);
  border-radius: 6px; padding: 4px 12px;
  font-size: 13px; color: var(--text-secondary);
  cursor: pointer; transition: var(--transition);
}

.copy-btn:hover { border-color: var(--accent); color: var(--accent); }
.copy-btn.copied { border-color: #34c77b; color: #34c77b; }

/* === Knowledge / Reference Section === */
.tool-knowledge {
  background: var(--bg-card);
  border-radius: var(--radius-lg);
  border: 1px solid var(--border);
  padding: 32px;
  box-shadow: var(--shadow-sm);
  margin-top: 24px;
}

.tool-knowledge h3 {
  font-size: 18px; font-weight: 600; color: var(--text-primary);
  margin-bottom: 16px; padding-bottom: 12px;
  border-bottom: 2px solid var(--accent-light);
  display: flex; align-items: center; gap: 8px;
}

.tool-knowledge h4 {
  font-size: 15px; font-weight: 600; color: var(--text-primary);
  margin: 20px 0 10px;
}

.tool-knowledge p {
  font-size: 14px; color: var(--text-secondary); line-height: 1.8;
  margin-bottom: 12px;
}

.tool-knowledge ul, .tool-knowledge ol {
  font-size: 14px; color: var(--text-secondary); line-height: 1.8;
  padding-left: 20px; margin-bottom: 12px;
}

.tool-knowledge li { margin-bottom: 4px; }

.tool-knowledge code {
  background: var(--accent-light); color: var(--accent);
  padding: 2px 6px; border-radius: 4px; font-size: 13px;
}

.tool-knowledge .formula-box {
  background: var(--bg-primary); border: 1px solid var(--border);
  border-radius: 8px; padding: 16px 20px; margin: 12px 0;
  font-family: 'Courier New', monospace; font-size: 15px;
  color: var(--text-primary); text-align: center;
  line-height: 2;
}

.tool-knowledge .ref-table {
  width: 100%; border-collapse: collapse; margin: 12px 0;
  font-size: 14px;
}

.tool-knowledge .ref-table th {
  background: var(--accent-light); color: var(--accent);
  font-weight: 600; padding: 10px 14px; text-align: left;
  border: 1px solid var(--border);
}

.tool-knowledge .ref-table td {
  padding: 10px 14px; border: 1px solid var(--border);
  color: var(--text-secondary);
}

.tool-knowledge .ref-table tr:hover td {
  background: rgba(102,126,234,.03);
}

.tool-knowledge .tip-box {
  background: #fff8e1; border-left: 4px solid #f59f00;
  border-radius: 0 8px 8px 0; padding: 14px 18px;
  margin: 16px 0; font-size: 14px; color: #6d5c00;
}

.tool-knowledge .tip-box strong { color: #e68a00; }

/* === Related Tools / Cross-linking === */
.related-tools-section {
  margin-top: 32px; padding-top: 0;
}

.related-tools-section h3 {
  font-size: 18px; font-weight: 600; color: var(--text-primary);
  margin-bottom: 16px; padding-bottom: 12px;
  border-bottom: 2px solid var(--accent-light);
  display: flex; align-items: center; gap: 8px;
}

.related-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(220px, 1fr));
  gap: 12px;
}

.related-card {
  display: flex; align-items: center; gap: 12px;
  background: var(--bg-card); border: 1px solid var(--border);
  border-radius: var(--radius); padding: 14px 16px;
  transition: var(--transition); cursor: pointer;
}

.related-card:hover {
  border-color: var(--accent);
  box-shadow: 0 4px 12px rgba(102,126,234,.12);
  transform: translateY(-1px);
}

.related-card .rc-icon {
  width: 38px; height: 38px; border-radius: 8px; flex-shrink: 0;
  display: flex; align-items: center; justify-content: center;
  font-size: 18px; background: var(--accent-light);
}

.related-card .rc-info { flex: 1; min-width: 0; }

.related-card .rc-name {
  font-size: 14px; font-weight: 600; color: var(--text-primary);
  white-space: nowrap; overflow: hidden; text-overflow: ellipsis;
}

.related-card .rc-desc {
  font-size: 12px; color: var(--text-muted);
  white-space: nowrap; overflow: hidden; text-overflow: ellipsis;
}

/* Popular tools bar at very bottom */
.popular-tools-bar {
  margin-top: 24px;
  background: var(--bg-card);
  border-radius: var(--radius-lg);
  border: 1px solid var(--border);
  padding: 24px 32px;
  box-shadow: var(--shadow-sm);
}

.popular-tools-bar h3 {
  font-size: 16px; font-weight: 600; color: var(--text-primary);
  margin-bottom: 14px;
}

.popular-tags {
  display: flex; flex-wrap: wrap; gap: 8px;
}

.popular-tag {
  display: inline-flex; align-items: center; gap: 4px;
  padding: 6px 14px; border-radius: 20px;
  border: 1px solid var(--border); background: var(--bg-primary);
  font-size: 13px; color: var(--text-secondary);
  transition: var(--transition); cursor: pointer;
}

.popular-tag:hover {
  border-color: var(--accent); color: var(--accent);
  background: var(--accent-light);
}

.popular-tag .pt-icon { font-size: 14px; }

/* Site footer for tool pages */
.tool-footer {
  max-width: 960px; margin: 32px auto 0; padding: 0 24px 40px;
  text-align: center; color: var(--text-muted); font-size: 13px;
}

.tool-footer a { color: var(--accent); }
.tool-footer a:hover { text-decoration: underline; }

@media (max-width: 640px) {
  .form-row { flex-direction: column; gap: 0; }
  .tool-body { padding: 0 16px; }
  .tool-card-main { padding: 20px; }
  .tool-knowledge { padding: 20px; }
  .popular-tools-bar { padding: 16px 20px; }
  .related-grid { grid-template-columns: 1fr; }
}