/* ========================================
   DSA Visualizer — Design System
   ======================================== */

@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700;800;900&family=JetBrains+Mono:wght@400;500;600&display=swap');

/* --- Design Tokens --- */
:root {
  /* Backgrounds */
  --bg-primary: #ffffff;
  --bg-secondary: #f8fafc;
  --bg-tertiary: #f1f5f9;
  --bg-card: #ffffff;
  --bg-glass: #ffffff;
  --bg-glass-hover: #f8fafc;
  --border-glass: #e2e8f0;
  --border-glass-hover: #cbd5e1;

  /* Text */
  --text-primary: #0f172a;
  --text-secondary: #475569;
  --text-muted: #64748b;
  --text-inverse: #ffffff;

  /* Accents */
  --accent-cyan: #0284c7;
  --accent-purple: #6366f1;
  --accent-pink: #e11d48;
  --accent-green: #16a34a;
  --accent-yellow: #ca8a04;
  --accent-orange: #ea580c;
  --accent-red: #dc2626;
  --accent-blue: #2563eb;

  /* Gradients */
  --gradient-primary: linear-gradient(135deg, #2563eb 0%, #4f46e5 100%);
  --gradient-secondary: linear-gradient(135deg, #4f46e5 0%, #e11d48 100%);
  --gradient-warm: linear-gradient(135deg, #ea580c 0%, #e11d48 100%);
  --gradient-cool: linear-gradient(135deg, #0284c7 0%, #16a34a 100%);
  --gradient-hero: linear-gradient(135deg, rgba(37,99,235,0.04) 0%, rgba(79,70,229,0.04) 50%, rgba(225,29,72,0.04) 100%);
  --gradient-text: linear-gradient(135deg, #2563eb, #4f46e5);

  /* Typography */
  --font-main: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', 'Cascadia Code', monospace;

  --fs-xs: 0.7rem;
  --fs-sm: 0.8rem;
  --fs-base: 0.925rem;
  --fs-md: 1.05rem;
  --fs-lg: 1.25rem;
  --fs-xl: 1.6rem;
  --fs-2xl: 2rem;
  --fs-3xl: 2.8rem;
  --fs-4xl: 3.8rem;

  --fw-light: 300;
  --fw-normal: 400;
  --fw-medium: 500;
  --fw-semibold: 600;
  --fw-bold: 700;
  --fw-black: 900;

  /* Spacing */
  --space-2xs: 0.15rem;
  --space-xs: 0.35rem;
  --space-sm: 0.65rem;
  --space-md: 1rem;
  --space-lg: 1.5rem;
  --space-xl: 2rem;
  --space-2xl: 3rem;
  --space-3xl: 4.5rem;
  --space-4xl: 6rem;

  /* Radius */
  --radius-xs: 4px;
  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 16px;
  --radius-xl: 24px;
  --radius-full: 9999px;

  /* Shadows */
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.08), 0 2px 4px -1px rgba(0, 0, 0, 0.04);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
  --shadow-glow-cyan: 0 4px 14px 0 rgba(37, 99, 235, 0.25);
  --shadow-glow-purple: 0 4px 14px 0 rgba(79, 70, 229, 0.25);
  --shadow-glow-pink: 0 4px 14px 0 rgba(225, 29, 72, 0.25);

  /* Transitions */
  --ease-out: cubic-bezier(0.16, 1, 0.3, 1);
  --ease-bounce: cubic-bezier(0.34, 1.56, 0.64, 1);
  --transition-fast: 150ms var(--ease-out);
  --transition-normal: 300ms var(--ease-out);
  --transition-slow: 500ms var(--ease-out);

  /* Layout */
  --sidebar-width: 260px;
  --header-height: 64px;
  --content-max-width: 1200px;
}

/* --- Reset & Base --- */
*,
*::before,
*::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

html {
  font-size: 16px;
  scroll-behavior: smooth;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  font-family: var(--font-main);
  font-size: var(--fs-base);
  font-weight: var(--fw-normal);
  color: var(--text-primary);
  background: var(--bg-primary);
  line-height: 1.6;
  min-height: 100vh;
  overflow-x: hidden;
}

a {
  color: var(--accent-cyan);
  text-decoration: none;
  transition: color var(--transition-fast);
}

a:hover {
  color: var(--accent-purple);
}

img {
  max-width: 100%;
  display: block;
}

button {
  cursor: pointer;
  font-family: var(--font-main);
  border: none;
  outline: none;
  background: none;
  color: inherit;
}

input, select, textarea {
  font-family: var(--font-main);
  color: var(--text-primary);
  background: var(--bg-glass);
  border: 1px solid var(--border-glass);
  border-radius: var(--radius-sm);
  padding: var(--space-sm) var(--space-md);
  font-size: var(--fs-sm);
  transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
  outline: none;
}

input:focus, select:focus, textarea:focus {
  border-color: var(--accent-cyan);
  box-shadow: 0 0 0 3px rgba(0, 212, 255, 0.1);
}

select {
  appearance: none;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='12' height='12' viewBox='0 0 12 12'%3E%3Cpath fill='%238b8ba8' d='M6 8L1 3h10z'/%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: right 12px center;
  padding-right: 32px;
  cursor: pointer;
}

::-webkit-scrollbar {
  width: 6px;
  height: 6px;
}
::-webkit-scrollbar-track {
  background: transparent;
}
::-webkit-scrollbar-thumb {
  background: rgba(0,0,0,0.15);
  border-radius: 3px;
}
::-webkit-scrollbar-thumb:hover {
  background: rgba(0,0,0,0.25);
}

/* --- Utility Classes --- */
.gradient-text {
  background: var(--gradient-text);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.text-center { text-align: center; }
.text-sm { font-size: var(--fs-sm); }
.text-xs { font-size: var(--fs-xs); }
.text-muted { color: var(--text-muted); }
.text-secondary { color: var(--text-secondary); }
.font-mono { font-family: var(--font-mono); }
.font-bold { font-weight: var(--fw-bold); }
.font-semibold { font-weight: var(--fw-semibold); }

.flex { display: flex; }
.flex-col { flex-direction: column; }
.items-center { align-items: center; }
.justify-center { justify-content: center; }
.justify-between { justify-content: space-between; }
.gap-sm { gap: var(--space-sm); }
.gap-md { gap: var(--space-md); }
.gap-lg { gap: var(--space-lg); }
.gap-xl { gap: var(--space-xl); }
.flex-1 { flex: 1; }
.flex-wrap { flex-wrap: wrap; }

.hidden { display: none !important; }
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  clip: rect(0,0,0,0);
  white-space: nowrap;
  border: 0;
}

/* --- Animations --- */
@keyframes fadeIn {
  from { opacity: 0; }
  to { opacity: 1; }
}

@keyframes fadeInUp {
  from { opacity: 0; transform: translateY(20px); }
  to { opacity: 1; transform: translateY(0); }
}

@keyframes fadeInDown {
  from { opacity: 0; transform: translateY(-20px); }
  to { opacity: 1; transform: translateY(0); }
}

@keyframes slideInRight {
  from { opacity: 0; transform: translateX(30px); }
  to { opacity: 1; transform: translateX(0); }
}

@keyframes slideInLeft {
  from { opacity: 0; transform: translateX(-30px); }
  to { opacity: 1; transform: translateX(0); }
}

@keyframes scaleIn {
  from { opacity: 0; transform: scale(0.9); }
  to { opacity: 1; transform: scale(1); }
}

@keyframes pulse {
  0%, 100% { opacity: 1; }
  50% { opacity: 0.5; }
}

@keyframes float {
  0%, 100% { transform: translateY(0); }
  50% { transform: translateY(-8px); }
}

@keyframes shimmer {
  0% { background-position: -200% center; }
  100% { background-position: 200% center; }
}

@keyframes gradientShift {
  0% { background-position: 0% 50%; }
  50% { background-position: 100% 50%; }
  100% { background-position: 0% 50%; }
}

@keyframes ripple {
  to { transform: scale(4); opacity: 0; }
}

@keyframes barGrow {
  from { transform: scaleY(0); }
  to { transform: scaleY(1); }
}

.animate-fade-in { animation: fadeIn 0.5s var(--ease-out) forwards; }
.animate-fade-in-up { animation: fadeInUp 0.6s var(--ease-out) forwards; }
.animate-scale-in { animation: scaleIn 0.4s var(--ease-out) forwards; }
.animate-float { animation: float 3s ease-in-out infinite; }

/* Stagger children */
.stagger-children > * {
  opacity: 0;
  animation: fadeInUp 0.5s var(--ease-out) forwards;
}
.stagger-children > *:nth-child(1) { animation-delay: 0.05s; }
.stagger-children > *:nth-child(2) { animation-delay: 0.1s; }
.stagger-children > *:nth-child(3) { animation-delay: 0.15s; }
.stagger-children > *:nth-child(4) { animation-delay: 0.2s; }
.stagger-children > *:nth-child(5) { animation-delay: 0.25s; }
.stagger-children > *:nth-child(6) { animation-delay: 0.3s; }
.stagger-children > *:nth-child(7) { animation-delay: 0.35s; }
.stagger-children > *:nth-child(8) { animation-delay: 0.4s; }

/* Page transition */
.page-section {
  display: none;
  opacity: 0;
}
.page-section.active {
  display: block;
  animation: fadeIn 0.35s var(--ease-out) forwards;
}

/* --- Background Effects --- */
.bg-grid {
  position: fixed;
  top: 0; left: 0; right: 0; bottom: 0;
  background-image:
    linear-gradient(rgba(0,0,0,0.03) 1px, transparent 1px),
    linear-gradient(90deg, rgba(0,0,0,0.03) 1px, transparent 1px);
  background-size: 60px 60px;
  pointer-events: none;
  z-index: 0;
}

.bg-glow {
  position: fixed;
  width: 600px;
  height: 600px;
  border-radius: 50%;
  filter: blur(120px);
  opacity: 0.08;
  pointer-events: none;
  z-index: 0;
}
.bg-glow--cyan {
  background: var(--accent-cyan);
  top: -200px;
  right: -100px;
}
.bg-glow--purple {
  background: var(--accent-purple);
  bottom: -200px;
  left: -100px;
}

/* --- Responsive --- */
@media (max-width: 768px) {
  :root {
    --fs-3xl: 2rem;
    --fs-4xl: 2.5rem;
    --sidebar-width: 0px;
  }
}