/* ============================================
   PROBABILITY VISUALIZER - DESIGN SYSTEM
   ============================================ */

:root {
  /* Color Palette */
  --bg-primary: #0a0a0f;
  --bg-secondary: #12121a;
  --bg-card: rgba(255, 255, 255, 0.05);
  --bg-glass: rgba(255, 255, 255, 0.08);
  
  --text-primary: #ffffff;
  --text-secondary: rgba(255, 255, 255, 0.7);
  --text-muted: rgba(255, 255, 255, 0.5);
  
  --accent-blue: #4f8cff;
  --accent-purple: #a855f7;
  --accent-pink: #ec4899;
  --accent-green: #10b981;
  --accent-orange: #f97316;
  --accent-yellow: #eab308;
  
  --gradient-primary: linear-gradient(135deg, #4f8cff 0%, #a855f7 50%, #ec4899 100%);
  --gradient-success: linear-gradient(135deg, #10b981 0%, #4f8cff 100%);
  --gradient-warm: linear-gradient(135deg, #f97316 0%, #ec4899 100%);
  
  /* Spacing */
  --space-xs: 0.25rem;
  --space-sm: 0.5rem;
  --space-md: 1rem;
  --space-lg: 1.5rem;
  --space-xl: 2rem;
  --space-2xl: 3rem;
  
  /* Border Radius */
  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 20px;
  --radius-full: 9999px;
  
  /* Shadows */
  --shadow-glow: 0 0 40px rgba(79, 140, 255, 0.3);
  --shadow-card: 0 8px 32px rgba(0, 0, 0, 0.4);
  
  /* Typography */
  --font-main: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', monospace;
}

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

html {
  font-size: 16px;
  scroll-behavior: smooth;
}

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

/* Animated Background */
.bg-animated {
  position: fixed;
  inset: 0;
  z-index: -1;
  background: var(--bg-primary);
  overflow: hidden;
}

.bg-animated::before {
  content: '';
  position: absolute;
  width: 150%;
  height: 150%;
  top: -25%;
  left: -25%;
  background: 
    radial-gradient(circle at 20% 80%, rgba(168, 85, 247, 0.15) 0%, transparent 50%),
    radial-gradient(circle at 80% 20%, rgba(79, 140, 255, 0.15) 0%, transparent 50%),
    radial-gradient(circle at 40% 40%, rgba(236, 72, 153, 0.1) 0%, transparent 40%);
  animation: bgFloat 20s ease-in-out infinite;
}

@keyframes bgFloat {
  0%, 100% { transform: translate(0, 0) rotate(0deg); }
  33% { transform: translate(2%, 2%) rotate(1deg); }
  66% { transform: translate(-1%, 1%) rotate(-1deg); }
}

/* Typography */
h1, h2, h3, h4, h5, h6 {
  font-weight: 700;
  line-height: 1.2;
}

h1 { font-size: 3rem; }
h2 { font-size: 2rem; }
h3 { font-size: 1.5rem; }
h4 { font-size: 1.25rem; }

.gradient-text {
  background: var(--gradient-primary);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

/* Container */
.container {
  width: 100%;
  max-width: 1400px;
  margin: 0 auto;
  padding: 0 var(--space-lg);
}

/* Glass Card */
.glass-card {
  background: var(--bg-glass);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  border: 1px solid rgba(255, 255, 255, 0.1);
  border-radius: var(--radius-lg);
  padding: var(--space-xl);
  box-shadow: var(--shadow-card);
  transition: all 0.3s ease;
}

.glass-card:hover {
  border-color: rgba(255, 255, 255, 0.2);
  transform: translateY(-4px);
  box-shadow: var(--shadow-glow);
}

/* Topic Cards */
.topic-card {
  position: relative;
  overflow: hidden;
}

.topic-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 4px;
  background: var(--gradient-primary);
  opacity: 0;
  transition: opacity 0.3s ease;
}

.topic-card:hover::before {
  opacity: 1;
}

.topic-card .topic-number {
  font-size: 4rem;
  font-weight: 800;
  background: var(--gradient-primary);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  opacity: 0.3;
  position: absolute;
  top: var(--space-md);
  right: var(--space-lg);
}

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-sm) var(--space-lg);
  border: none;
  border-radius: var(--radius-full);
  font-family: inherit;
  font-size: 0.95rem;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.3s ease;
  text-decoration: none;
}

.btn-primary {
  background: var(--gradient-primary);
  color: white;
}

.btn-primary:hover {
  transform: scale(1.05);
  box-shadow: 0 0 30px rgba(168, 85, 247, 0.5);
}

.btn-ghost {
  background: transparent;
  color: var(--text-primary);
  border: 1px solid rgba(255, 255, 255, 0.2);
}

.btn-ghost:hover {
  background: var(--bg-glass);
  border-color: rgba(255, 255, 255, 0.4);
}

/* Input & Sliders */
.input-group {
  display: flex;
  flex-direction: column;
  gap: var(--space-xs);
}

.input-group label {
  font-size: 0.875rem;
  color: var(--text-secondary);
  font-weight: 500;
}

input[type="range"] {
  -webkit-appearance: none;
  appearance: none;
  width: 100%;
  height: 8px;
  background: rgba(255, 255, 255, 0.1);
  border-radius: var(--radius-full);
  outline: none;
}

input[type="range"]::-webkit-slider-thumb {
  -webkit-appearance: none;
  appearance: none;
  width: 20px;
  height: 20px;
  background: var(--gradient-primary);
  border-radius: 50%;
  cursor: pointer;
  box-shadow: 0 0 15px rgba(168, 85, 247, 0.5);
}

input[type="number"], input[type="text"] {
  background: rgba(255, 255, 255, 0.05);
  border: 1px solid rgba(255, 255, 255, 0.1);
  border-radius: var(--radius-sm);
  padding: var(--space-sm) var(--space-md);
  color: var(--text-primary);
  font-family: var(--font-mono);
  font-size: 1rem;
  outline: none;
  transition: border-color 0.3s ease;
}

input[type="number"]:focus, input[type="text"]:focus {
  border-color: var(--accent-purple);
}

/* Visualization Canvas */
.viz-container {
  position: relative;
  background: rgba(0, 0, 0, 0.3);
  border-radius: var(--radius-md);
  border: 1px solid rgba(255, 255, 255, 0.1);
  overflow: hidden;
  min-height: 400px;
}

.viz-canvas {
  display: block;
  width: 100%;
  height: 100%;
}

/* Formula Display */
.formula-box {
  background: rgba(0, 0, 0, 0.4);
  border-radius: var(--radius-md);
  padding: var(--space-lg);
  font-family: var(--font-mono);
  font-size: 1.25rem;
  text-align: center;
  border: 1px solid rgba(255, 255, 255, 0.1);
}

.formula-box .highlight {
  color: var(--accent-purple);
  font-weight: 600;
}

.formula-box .result {
  color: var(--accent-green);
  font-weight: 700;
}

/* Stats Display */
.stats-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
  gap: var(--space-md);
}

.stat-item {
  text-align: center;
  padding: var(--space-md);
  background: rgba(255, 255, 255, 0.03);
  border-radius: var(--radius-md);
}

.stat-value {
  font-size: 2rem;
  font-weight: 700;
  font-family: var(--font-mono);
  background: var(--gradient-primary);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.stat-label {
  font-size: 0.875rem;
  color: var(--text-muted);
  margin-top: var(--space-xs);
}

/* Navigation */
.nav-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: var(--space-lg) 0;
  border-bottom: 1px solid rgba(255, 255, 255, 0.1);
  margin-bottom: var(--space-xl);
}

.nav-logo {
  font-size: 1.5rem;
  font-weight: 800;
  text-decoration: none;
  color: var(--text-primary);
}

.nav-breadcrumb {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  color: var(--text-muted);
  font-size: 0.875rem;
}

.nav-breadcrumb a {
  color: var(--text-secondary);
  text-decoration: none;
  transition: color 0.3s ease;
}

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

/* Grid Layouts */
.grid-topics {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
  gap: var(--space-xl);
}

.grid-problems {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: var(--space-md);
}

/* Problem Link Cards */
.problem-link {
  display: block;
  padding: var(--space-md) var(--space-lg);
  background: rgba(255, 255, 255, 0.03);
  border: 1px solid rgba(255, 255, 255, 0.08);
  border-radius: var(--radius-md);
  text-decoration: none;
  color: var(--text-primary);
  transition: all 0.3s ease;
}

.problem-link:hover {
  background: rgba(255, 255, 255, 0.08);
  border-color: var(--accent-purple);
  transform: translateX(8px);
}

.problem-link .problem-id {
  font-family: var(--font-mono);
  font-size: 0.875rem;
  color: var(--accent-purple);
  margin-bottom: var(--space-xs);
}

.problem-link .difficulty {
  display: inline-block;
  padding: 2px 8px;
  border-radius: var(--radius-full);
  font-size: 0.75rem;
  font-weight: 600;
  margin-left: var(--space-sm);
}

.difficulty-easy { background: rgba(16, 185, 129, 0.2); color: var(--accent-green); }
.difficulty-normal { background: rgba(234, 179, 8, 0.2); color: var(--accent-yellow); }
.difficulty-hard { background: rgba(249, 115, 22, 0.2); color: var(--accent-orange); }
.difficulty-expert { background: rgba(236, 72, 153, 0.2); color: var(--accent-pink); }

/* Animations */
@keyframes fadeIn {
  from { opacity: 0; transform: translateY(20px); }
  to { opacity: 1; transform: translateY(0); }
}

@keyframes pulse {
  0%, 100% { transform: scale(1); }
  50% { transform: scale(1.05); }
}

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

.animate-fade-in {
  animation: fadeIn 0.6s ease-out forwards;
}

.animate-pulse {
  animation: pulse 2s ease-in-out infinite;
}

/* Venn Diagram Specific */
.venn-circle {
  fill-opacity: 0.3;
  stroke-width: 3;
  transition: all 0.3s ease;
}

.venn-circle.set-a {
  fill: var(--accent-blue);
  stroke: var(--accent-blue);
}

.venn-circle.set-b {
  fill: var(--accent-pink);
  stroke: var(--accent-pink);
}

.venn-intersection {
  fill: var(--accent-purple);
  fill-opacity: 0.5;
}

/* Probability Bar */
.prob-bar-container {
  height: 40px;
  background: rgba(255, 255, 255, 0.1);
  border-radius: var(--radius-sm);
  overflow: hidden;
  position: relative;
}

.prob-bar {
  height: 100%;
  background: var(--gradient-primary);
  transition: width 0.5s ease;
  display: flex;
  align-items: center;
  justify-content: flex-end;
  padding-right: var(--space-md);
  font-weight: 600;
}

/* Step-by-step Proof */
.proof-steps {
  display: flex;
  flex-direction: column;
  gap: var(--space-md);
}

.proof-step {
  display: flex;
  gap: var(--space-md);
  padding: var(--space-md);
  background: rgba(255, 255, 255, 0.03);
  border-radius: var(--radius-md);
  border-left: 3px solid var(--accent-purple);
  opacity: 0.5;
  transition: all 0.3s ease;
}

.proof-step.active {
  opacity: 1;
  background: rgba(168, 85, 247, 0.1);
}

.proof-step-number {
  width: 28px;
  height: 28px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--gradient-primary);
  border-radius: 50%;
  font-weight: 700;
  font-size: 0.875rem;
  flex-shrink: 0;
}

/* Responsive */
@media (max-width: 768px) {
  h1 { font-size: 2rem; }
  h2 { font-size: 1.5rem; }
  
  .container {
    padding: 0 var(--space-md);
  }
  
  .glass-card {
    padding: var(--space-lg);
  }
  
  .grid-topics {
    grid-template-columns: 1fr;
  }
}