:root {
  /* Swiss Design Color Palette */
  --swiss-black: #0a0a0a;
  --swiss-white: #ffffff;
  --swiss-offwhite: #fafafa;
  --swiss-gray-100: #f5f5f5;
  --swiss-gray-200: #e5e5e5;
  --swiss-gray-300: #d4d4d4;
  --swiss-gray-400: #a3a3a3;
  --swiss-gray-500: #737373;
  --swiss-gray-600: #525252;
  --swiss-gray-700: #404040;
  --swiss-gray-800: #262626;
  --swiss-gray-900: #171717;
  
  /* Accent - Vermilion Red (Swiss International Style) */
  --swiss-accent: #ff3b00;
  --swiss-accent-dark: #cc2f00;
  --swiss-accent-light: #ff6b3d;
  
  /* Typography Scale - Major Third (1.25) */
  --text-xs: 0.75rem;
  --text-sm: 0.875rem;
  --text-base: 1rem;
  --text-lg: 1.125rem;
  --text-xl: 1.25rem;
  --text-2xl: 1.5rem;
  --text-3xl: 1.875rem;
  --text-4xl: 2.25rem;
  --text-5xl: 3rem;
  --text-6xl: 3.75rem;
  --text-7xl: 4.5rem;
  
  /* Spacing - 8px base unit */
  --space-1: 0.25rem;
  --space-2: 0.5rem;
  --space-3: 0.75rem;
  --space-4: 1rem;
  --space-5: 1.25rem;
  --space-6: 1.5rem;
  --space-8: 2rem;
  --space-10: 2.5rem;
  --space-12: 3rem;
  --space-16: 4rem;
  --space-20: 5rem;
  --space-24: 6rem;
  --space-32: 8rem;
  --space-40: 10rem;
  --space-48: 12rem;
  
  /* Layout */
  --max-width: 1440px;
  --content-width: 720px;
  --sidebar-width: 280px;
  
  /* Swiss Grid - Asymmetric */
  --grid-columns: 12;
  --grid-gap: 1.5rem;
  
  /* Animation */
  --transition-fast: 150ms cubic-bezier(0.4, 0, 0.2, 1);
  --transition-base: 300ms cubic-bezier(0.4, 0, 0.2, 1);
  --transition-slow: 500ms cubic-bezier(0.4, 0, 0.2, 1);
  
  /* Z-index scale */
  --z-dropdown: 100;
  --z-sticky: 200;
  --z-fixed: 300;
  --z-modal-backdrop: 400;
  --z-modal: 500;
  --z-popover: 600;
  --z-tooltip: 700;
}

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

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

body {
  font-family: 'IBM Plex Sans', -apple-system, BlinkMacSystemFont, sans-serif;
  font-size: var(--text-base);
  line-height: 1.6;
  color: var(--swiss-black);
  background-color: var(--swiss-white);
  overflow-x: hidden;
}

/* Typography - Neue Montreal for Display */
@font-face {
  font-family: 'Neue Montreal';
  src: url('../assets/fonts/NeueMontreal-Regular.woff2') format('woff2');
  font-weight: 400;
  font-style: normal;
  font-display: swap;
}

@font-face {
  font-family: 'Neue Montreal';
  src: url('../assets/fonts/NeueMontreal-Bold.woff2') format('woff2');
  font-weight: 700;
  font-style: normal;
  font-display: swap;
}

h1, h2, h3, .display {
  font-family: 'Neue Montreal', 'IBM Plex Sans', sans-serif;
  font-weight: 700;
  line-height: 1.1;
  letter-spacing: -0.02em;
}

h1 {
  font-size: var(--text-6xl);
}

h2 {
  font-size: var(--text-4xl);
}

h3 {
  font-size: var(--text-2xl);
}

p {
  margin-bottom: var(--space-4);
  max-width: 65ch;
}

/* Swiss Grid System */
.swiss-grid {
  display: grid;
  grid-template-columns: repeat(var(--grid-columns), 1fr);
  gap: var(--grid-gap);
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--space-6);
}

/* Asymmetric layouts */
.swiss-asymmetric {
  display: grid;
  grid-template-columns: 1fr 1.618fr;
  gap: var(--space-16);
}

.swiss-asymmetric-reverse {
  display: grid;
  grid-template-columns: 1.618fr 1fr;
  gap: var(--space-16);
}

/* Swiss Components */
.swiss-section {
  padding: var(--space-24) 0;
  position: relative;
}

.swiss-section::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 1px;
  background: linear-gradient(90deg, var(--swiss-accent) 0%, transparent 100%);
}

.swiss-card {
  background: var(--swiss-white);
  border: 1px solid var(--swiss-gray-200);
  padding: var(--space-8);
  transition: transform var(--transition-base), box-shadow var(--transition-base);
}

.swiss-card:hover {
  transform: translateY(-2px);
  box-shadow: 0 8px 30px rgba(0, 0, 0, 0.08);
}

/* Accent Elements */
.swiss-accent-line {
  width: 60px;
  height: 3px;
  background-color: var(--swiss-accent);
  margin: var(--space-6) 0;
}

.swiss-accent-text {
  color: var(--swiss-accent);
}

.swiss-tag {
  display: inline-block;
  padding: var(--space-1) var(--space-3);
  font-size: var(--text-xs);
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  border: 1px solid var(--swiss-black);
  color: var(--swiss-black);
}

.swiss-tag-accent {
  background-color: var(--swiss-accent);
  border-color: var(--swiss-accent);
  color: var(--swiss-white);
}

/* Buttons */
.swiss-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: var(--space-3) var(--space-6);
  font-family: 'Neue Montreal', sans-serif;
  font-size: var(--text-sm);
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  border: 2px solid var(--swiss-black);
  background-color: var(--swiss-white);
  color: var(--swiss-black);
  cursor: pointer;
  transition: all var(--transition-fast);
  text-decoration: none;
}

.swiss-btn:hover {
  background-color: var(--swiss-black);
  color: var(--swiss-white);
}

.swiss-btn-accent {
  background-color: var(--swiss-accent);
  border-color: var(--swiss-accent);
  color: var(--swiss-white);
}

.swiss-btn-accent:hover {
  background-color: var(--swiss-accent-dark);
  border-color: var(--swiss-accent-dark);
}

/* Navigation */
.swiss-nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: var(--z-fixed);
  background-color: rgba(255, 255, 255, 0.95);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--swiss-gray-200);
}

.swiss-nav-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: var(--space-4) var(--space-6);
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.swiss-logo {
  font-family: 'Neue Montreal', sans-serif;
  font-size: var(--text-xl);
  font-weight: 700;
  text-decoration: none;
  color: var(--swiss-black);
}

.swiss-logo span {
  color: var(--swiss-accent);
}

/* Level Navigation */
.level-nav {
  display: flex;
  gap: var(--space-2);
  list-style: none;
}

.level-nav a {
  display: block;
  padding: var(--space-2) var(--space-3);
  font-size: var(--text-sm);
  font-weight: 600;
  text-decoration: none;
  color: var(--swiss-gray-600);
  border-bottom: 2px solid transparent;
  transition: all var(--transition-fast);
}

.level-nav a:hover,
.level-nav a.active {
  color: var(--swiss-black);
  border-bottom-color: var(--swiss-accent);
}

/* Mode Switchers */
.mode-switcher {
  position: fixed;
  bottom: var(--space-6);
  right: var(--space-6);
  z-index: var(--z-fixed);
  display: flex;
  flex-direction: column;
  gap: var(--space-3);
}

.mode-pill {
  display: flex;
  align-items: center;
  background-color: var(--swiss-white);
  border: 1px solid var(--swiss-gray-300);
  border-radius: 100px;
  padding: var(--space-1);
  box-shadow: 0 2px 10px rgba(0, 0, 0, 0.1);
}

.mode-option {
  padding: var(--space-2) var(--space-4);
  font-size: var(--text-xs);
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  cursor: pointer;
  border-radius: 100px;
  transition: all var(--transition-fast);
  color: var(--swiss-gray-500);
}

.mode-option.active {
  background-color: var(--swiss-accent);
  color: var(--swiss-white);
}

.mode-option:hover:not(.active) {
  color: var(--swiss-black);
}

/* Content Areas */
.content-casual {
  display: block; /* Show by default, JS will handle switching */
}

.content-formal {
  display: none; /* Hidden by default */
}

/* When formal is active, hide casual and show formal */
body.mode-formal .content-casual {
  display: none;
}

body.mode-formal .content-formal {
  display: block;
}

/* Legacy active class support */
.content-casual.active {
  display: block;
}

.content-formal.active {
  display: block;
}

/* Code Blocks */
.code-tabs {
  display: flex;
  gap: var(--space-1);
  margin-bottom: var(--space-2);
  border-bottom: 1px solid var(--swiss-gray-300);
}

.code-tab {
  padding: var(--space-2) var(--space-4);
  font-size: var(--text-sm);
  font-weight: 600;
  cursor: pointer;
  border-bottom: 2px solid transparent;
  transition: all var(--transition-fast);
  color: var(--swiss-gray-500);
}

.code-tab.active {
  color: var(--swiss-accent);
  border-bottom-color: var(--swiss-accent);
}

.code-block {
  background-color: var(--swiss-gray-900);
  color: var(--swiss-gray-100);
  padding: var(--space-6);
  border-radius: 0;
  overflow-x: auto;
  font-family: 'IBM Plex Mono', 'Fira Code', monospace;
  font-size: var(--text-sm);
  line-height: 1.7;
}

/* Visualization Container */
.viz-container {
  background-color: var(--swiss-gray-100);
  border: 1px solid var(--swiss-gray-200);
  padding: var(--space-6);
  margin: var(--space-8) 0;
  position: relative;
}

.viz-toggle {
  position: absolute;
  top: var(--space-4);
  right: var(--space-4);
  display: flex;
  gap: var(--space-1);
}

.viz-option {
  padding: var(--space-1) var(--space-3);
  font-size: var(--text-xs);
  font-weight: 600;
  cursor: pointer;
  border: 1px solid var(--swiss-gray-300);
  background-color: var(--swiss-white);
  transition: all var(--transition-fast);
}

.viz-option.active {
  background-color: var(--swiss-accent);
  border-color: var(--swiss-accent);
  color: var(--swiss-white);
}

/* Progress Indicators */
.progress-tracker {
  position: fixed;
  left: var(--space-6);
  top: 50%;
  transform: translateY(-50%);
  z-index: var(--z-sticky);
}

.progress-dot {
  width: 12px;
  height: 12px;
  border-radius: 50%;
  border: 2px solid var(--swiss-gray-300);
  background-color: var(--swiss-white);
  margin-bottom: var(--space-3);
  cursor: pointer;
  transition: all var(--transition-fast);
}

.progress-dot.completed {
  background-color: var(--swiss-accent);
  border-color: var(--swiss-accent);
}

.progress-dot.current {
  border-color: var(--swiss-accent);
  box-shadow: 0 0 0 3px rgba(255, 59, 0, 0.2);
}

/* Hero Section */
.hero {
  min-height: 100vh;
  display: flex;
  align-items: center;
  padding-top: 80px;
  background-color: var(--swiss-offwhite);
  position: relative;
  overflow: hidden;
}

.hero::after {
  content: '';
  position: absolute;
  right: -10%;
  top: -10%;
  width: 60%;
  height: 120%;
  background: linear-gradient(135deg, transparent 0%, rgba(255, 59, 0, 0.03) 100%);
  transform: skewX(-5deg);
}

.hero-content {
  max-width: var(--content-width);
  position: relative;
  z-index: 1;
}

.hero h1 {
  font-size: clamp(var(--text-4xl), 8vw, var(--text-7xl));
  margin-bottom: var(--space-6);
  line-height: 0.95;
}

.hero-subtitle {
  font-size: var(--text-xl);
  color: var(--swiss-gray-600);
  margin-bottom: var(--space-8);
  max-width: 50ch;
}

/* Level Cards Grid */
.levels-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
  gap: var(--space-6);
  margin-top: var(--space-12);
}

.level-card {
  position: relative;
  padding: var(--space-8);
  background-color: var(--swiss-white);
  border: 1px solid var(--swiss-gray-200);
  transition: all var(--transition-base);
  cursor: pointer;
  text-decoration: none;
  color: inherit;
  display: block;
}

.level-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  width: 4px;
  height: 100%;
  background-color: var(--swiss-accent);
  transform: scaleY(0);
  transition: transform var(--transition-base);
}

.level-card:hover::before {
  transform: scaleY(1);
}

.level-card:hover {
  transform: translateY(-4px);
  box-shadow: 0 12px 40px rgba(0, 0, 0, 0.1);
}

.level-number {
  font-family: 'Neue Montreal', sans-serif;
  font-size: var(--text-5xl);
  font-weight: 700;
  color: var(--swiss-gray-200);
  line-height: 1;
  margin-bottom: var(--space-4);
}

.level-card:hover .level-number {
  color: var(--swiss-accent);
}

.level-title {
  font-size: var(--text-xl);
  font-weight: 700;
  margin-bottom: var(--space-2);
}

.level-description {
  font-size: var(--text-sm);
  color: var(--swiss-gray-600);
}

/* Utility Classes */
.text-center { text-align: center; }
.text-right { text-align: right; }
.mt-0 { margin-top: 0; }
.mb-0 { margin-bottom: 0; }
.ml-auto { margin-left: auto; }
.mr-auto { margin-right: auto; }

/* Animation Classes */
.fade-in {
  opacity: 0;
  transform: translateY(20px);
  transition: opacity var(--transition-slow), transform var(--transition-slow);
}

.fade-in.visible {
  opacity: 1;
  transform: translateY(0);
}

/* Scroll Reveal */
.reveal {
  opacity: 0;
  transform: translateY(30px);
  transition: opacity 0.8s ease, transform 0.8s ease;
}

.reveal.active {
  opacity: 1;
  transform: translateY(0);
}

/* Math Display */
.math-block {
  background-color: var(--swiss-gray-100);
  padding: var(--space-6);
  margin: var(--space-6) 0;
  overflow-x: auto;
}

.math-simple,
.math-complex {
  display: none;
}

.math-simple.active,
.math-complex.active {
  display: block;
}

/* Figure Styling */
.figure-container {
  margin: var(--space-8) 0;
  text-align: center;
}

.figure-container img {
  max-width: 100%;
  height: auto;
  border: 1px solid var(--swiss-gray-200);
}

.figure-caption {
  font-size: var(--text-sm);
  color: var(--swiss-gray-600);
  margin-top: var(--space-3);
  font-style: italic;
}

/* Simple/Complex Toggle */
.explanation-toggle {
  display: flex;
  gap: var(--space-2);
  margin: var(--space-4) 0;
}

.explanation-btn {
  padding: var(--space-2) var(--space-4);
  font-size: var(--text-sm);
  font-weight: 600;
  cursor: pointer;
  border: 1px solid var(--swiss-gray-300);
  background-color: var(--swiss-white);
  transition: all var(--transition-fast);
}

.explanation-btn.active {
  background-color: var(--swiss-accent);
  border-color: var(--swiss-accent);
  color: var(--swiss-white);
}

/* Print Styles */
@media print {
  .swiss-nav,
  .mode-switcher,
  .progress-tracker {
    display: none;
  }
  
  body {
    font-size: 11pt;
    line-height: 1.5;
  }
}