:root {
  --primary: #2563eb;
  --primary-dark: #1d4ed8;
  --primary-light: #eff6ff;
  --secondary: #64748b;
  --success: #16a34a;
  --warning: #d97706;
  --danger: #dc2626;
  --india: #f97316;
  --india-light: #fff7ed;

  --bg: #ffffff;
  --bg-secondary: #f8fafc;
  --bg-tertiary: #f1f5f9;
  --border: #e2e8f0;
  --border-hover: #cbd5e1;
  --text: #0f172a;
  --text-secondary: #475569;
  --text-muted: #94a3b8;

  --font: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
  --radius: 8px;
  --radius-lg: 12px;
  --radius-xl: 16px;
  --shadow: 0 1px 3px rgba(0,0,0,0.08), 0 1px 2px rgba(0,0,0,0.04);
  --shadow-md: 0 4px 6px rgba(0,0,0,0.07), 0 2px 4px rgba(0,0,0,0.04);
  --shadow-lg: 0 10px 15px rgba(0,0,0,0.08), 0 4px 6px rgba(0,0,0,0.04);

  --header-height: 64px;
  --sidebar-width: 260px;
  --content-max: 860px;
  --page-max: 1200px;

  /* Category colors */
  --cat-maths: #2563eb;
  --cat-finance: #16a34a;
  --cat-unit: #d97706;
  --cat-health: #9333ea;
  --cat-datetime: #0891b2;
  --cat-science: #dc2626;
  --cat-india: #f97316;
}

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

html { font-size: 16px; scroll-behavior: smooth; -webkit-text-size-adjust: 100%; }

body {
  font-family: var(--font);
  font-size: 1rem;
  line-height: 1.7;
  color: var(--text);
  background: var(--bg);
  -webkit-font-smoothing: antialiased;
}

h1 { font-size: clamp(1.6rem, 4vw, 2rem); font-weight: 700; line-height: 1.25; color: var(--text); }
h2 { font-size: clamp(1.25rem, 3vw, 1.5rem); font-weight: 600; line-height: 1.3; }
h3 { font-size: 1.25rem; font-weight: 600; line-height: 1.4; }
h4 { font-size: 1.1rem; font-weight: 600; }
p { margin-bottom: 1rem; }
p:last-child { margin-bottom: 0; }
a { color: var(--primary); text-decoration: none; }
a:hover { text-decoration: underline; }
img { max-width: 100%; height: auto; display: block; }
ul, ol { padding-left: 1.5rem; }
li { margin-bottom: 0.35rem; }

.sr-only {
  position: absolute; width: 1px; height: 1px;
  padding: 0; margin: -1px; overflow: hidden;
  clip: rect(0,0,0,0); white-space: nowrap; border: 0;
}

/* Skip to content */
.skip-link {
  position: absolute; top: -100%; left: 1rem;
  background: var(--primary); color: #fff;
  padding: 0.5rem 1rem; border-radius: var(--radius);
  z-index: 9999; font-weight: 600;
  transition: top 0.2s;
}
.skip-link:focus { top: 1rem; }