:root {
  --primary: #1a56db;
  --primary-dark: #1e40af;
  --primary-light: #e8effc;
  --bg: #ffffff;
  --text: #1f2937;
  --text-light: #6b7280;
  --text-lighter: #9ca3af;
  --border: #e5e7eb;
  --shadow: 0 1px 3px rgba(0,0,0,0.06);
  --shadow-hover: 0 2px 8px rgba(0,0,0,0.08);
  --radius: 8px;
  --font: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Noto Sans SC', 'PingFang SC', sans-serif;
  --mono: 'SF Mono', 'Fira Code', Consolas, monospace;
}

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

body {
  font-family: var(--font);
  color: var(--text);
  background: var(--bg);
  line-height: 1.6;
  font-size: 15px;
  -webkit-font-smoothing: antialiased;
}

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

/* ===== Header ===== */
.header {
  text-align: center;
  padding: 48px 24px 32px;
}
.header h1 {
  font-size: 28px;
  font-weight: 700;
  letter-spacing: -0.5px;
  margin-bottom: 6px;
}
.header-desc {
  font-size: 14px;
  color: var(--text-light);
}

/* ===== Main ===== */
.main {
  max-width: 640px;
  margin: 0 auto;
  padding: 0 24px 48px;
}

/* ===== Search ===== */
.search-box {
  margin-bottom: 24px;
}
.search-box input {
  width: 100%;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 10px 16px;
  font-size: 15px;
  font-family: var(--font);
  color: var(--text);
  outline: none;
  transition: border-color 0.2s;
}
.search-box input:focus {
  border-color: var(--primary);
}
.search-box input::placeholder {
  color: var(--text-lighter);
}

/* ===== Category Filter ===== */
.category-filter {
  display: flex;
  gap: 6px;
  flex-wrap: wrap;
  margin-bottom: 24px;
}
.cat-btn {
  background: none;
  color: var(--text-light);
  border: 1px solid var(--border);
  padding: 4px 12px;
  border-radius: 6px;
  font-size: 13px;
  cursor: pointer;
  font-family: var(--font);
  transition: all 0.15s;
}
.cat-btn:hover {
  border-color: var(--primary);
  color: var(--primary);
}
.cat-btn.active {
  background: var(--primary);
  color: white;
  border-color: var(--primary);
}

/* ===== List Header ===== */
.list-header {
  margin-bottom: 12px;
}
.list-count {
  font-size: 13px;
  color: var(--text-lighter);
}

/* ===== Cards ===== */
.cheatsheet-grid {
  display: grid;
  gap: 12px;
}
.cheatsheet-card {
  display: block;
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 16px;
  text-decoration: none;
  color: var(--text);
  transition: border-color 0.15s, box-shadow 0.15s;
}
.cheatsheet-card:hover {
  border-color: var(--primary);
  box-shadow: var(--shadow-hover);
  text-decoration: none;
}
.card-cat {
  font-size: 12px;
  color: var(--text-lighter);
  margin-bottom: 4px;
}
.card-name {
  font-size: 16px;
  font-weight: 600;
  margin-bottom: 4px;
}
.card-desc {
  font-size: 13px;
  color: var(--text-light);
  line-height: 1.5;
  margin-bottom: 10px;
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
  overflow: hidden;
}
.card-meta {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 12px;
  flex-wrap: wrap;
}
.card-tag {
  background: #f3f4f6;
  color: var(--text-light);
  padding: 2px 8px;
  border-radius: 4px;
  font-size: 11px;
}
.card-date {
  color: var(--text-lighter);
}

/* ===== Empty ===== */
.empty-state {
  text-align: center;
  padding: 48px 20px;
  color: var(--text-lighter);
  font-size: 14px;
}

/* ===== Footer ===== */
.footer {
  text-align: center;
  padding: 24px;
  font-size: 13px;
  color: var(--text-lighter);
  border-top: 1px solid var(--border);
}
.footer a { color: var(--text-light); }

/* ===== Responsive ===== */
@media (max-width: 640px) {
  .header { padding: 36px 20px 24px; }
  .main { padding: 0 16px 36px; }
}

/* ===== Category colors (used on card labels) ===== */
.cat-python  { background: #e8effc; color: #1d4ed8; }
.cat-aiml    { background: #f3e8ff; color: #7c3aed; }
.cat-git     { background: #fef9c3; color: #a16207; }
.cat-rust    { background: #fce7f3; color: #be185d; }
.cat-math    { background: #d1fae5; color: #047857; }
.cat-db      { background: #e0e7ff; color: #4338ca; }
.cat-fe      { background: #ffe4e6; color: #e11d48; }
.cat-be      { background: #ccfbf1; color: #0f766e; }
.cat-devops  { background: #f3e8ff; color: #7c3aed; }
.cat-algo    { background: #fee2e2; color: #dc2626; }
.cat-default { background: #f3f4f6; color: #374151; }