:root {
  --background: 210 45% 98%;
  --foreground: 222 47% 12%;
  --primary: 252 87% 58%;
  --primary-foreground: 0 0% 100%;
  --secondary: 178 70% 42%;
  --secondary-foreground: 222 47% 9%;
  --muted: 218 24% 91%;
  --muted-foreground: 220 14% 42%;
  --destructive: 0 78% 58%;
  --destructive-foreground: 0 0% 100%;
  --border: 220 20% 84%;
  --card: 0 0% 100%;
  --card-foreground: 222 47% 12%;
  --shadow-sm: 0 4px 14px hsl(222 47% 12% / 0.08);
  --shadow-md: 0 14px 35px hsl(222 47% 12% / 0.12);
  --shadow-lg: 0 28px 70px hsl(252 87% 30% / 0.20);
  --transition-fast: 160ms ease;
  --transition-smooth: 280ms cubic-bezier(.2,.8,.2,1);
  --radius-sm: 0.65rem;
  --radius-md: 1rem;
  --radius-lg: 1.5rem;
}

.dark {
  --background: 230 30% 7%;
  --foreground: 220 35% 96%;
  --primary: 258 95% 70%;
  --primary-foreground: 240 20% 8%;
  --secondary: 179 75% 53%;
  --secondary-foreground: 230 30% 7%;
  --muted: 230 22% 16%;
  --muted-foreground: 221 16% 72%;
  --destructive: 0 82% 64%;
  --destructive-foreground: 0 0% 100%;
  --border: 228 18% 24%;
  --card: 230 24% 11%;
  --card-foreground: 220 35% 96%;
  --shadow-sm: 0 4px 14px hsl(0 0% 0% / 0.22);
  --shadow-md: 0 14px 35px hsl(0 0% 0% / 0.32);
  --shadow-lg: 0 28px 70px hsl(258 95% 15% / 0.45);
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  min-height: 100vh;
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  background:
    radial-gradient(circle at 15% 10%, hsl(var(--primary) / 0.16), transparent 28rem),
    radial-gradient(circle at 85% 20%, hsl(var(--secondary) / 0.14), transparent 24rem),
    hsl(var(--background));
  color: hsl(var(--foreground));
}

a { color: inherit; text-decoration: none; }
button, input, select, textarea { font: inherit; }
button { cursor: pointer; }

.focus-ring:focus-visible {
  outline: 3px solid hsl(var(--primary) / 0.34);
  outline-offset: 3px;
}

.glass {
  background: hsl(var(--card) / 0.78);
  backdrop-filter: blur(18px);
  border: 1px solid hsl(var(--border) / 0.85);
}

.math-grid {
  background-image:
    linear-gradient(hsl(var(--border) / 0.45) 1px, transparent 1px),
    linear-gradient(90deg, hsl(var(--border) / 0.45) 1px, transparent 1px);
  background-size: 28px 28px;
}

.formula {
  font-family: "STIX Two Math", Cambria Math, Georgia, serif;
}

::-webkit-scrollbar { width: 10px; }
::-webkit-scrollbar-track { background: hsl(var(--muted)); }
::-webkit-scrollbar-thumb { background: hsl(var(--primary) / 0.45); border-radius: 999px; }
::-webkit-scrollbar-thumb:hover { background: hsl(var(--primary) / 0.65); }