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

/* ===================================
           DEFINING CSS VARIABLES
           =================================== */
:root {
  /* Colors */
  --color-primary: #4a90e2;
  --color-secondary: #e94560;
  --color-success: #2ecc71;
  --color-warning: #f39c12;
  --color-dark: #1a1a2e;
  --color-light: #f5f5f5;
  --color-text: #333;
  --color-text-light: #666;

  /* Spacing */
  --spacing-small: 8px;
  --spacing-medium: 16px;
  --spacing-large: 24px;
  --spacing-xl: 32px;

  /* Border Radius */
  --radius-small: 4px;
  --radius-medium: 8px;
  --radius-large: 16px;
  --radius-circle: 50%;

  /* Font Sizes */
  --font-small: 12px;
  --font-base: 16px;
  --font-large: 20px;
  --font-xl: 24px;
  --font-xxl: 32px;

  /* Shadows */
  --shadow-small: 0 2px 4px rgba(0, 0, 0, 0.1);
  --shadow-medium: 0 4px 8px rgba(0, 0, 0, 0.1);
  --shadow-large: 0 8px 16px rgba(0, 0, 0, 0.1);

  /* Transitions */
  --transition-fast: 0.2s ease;
  --transition-normal: 0.3s ease;
  --transition-slow: 0.5s ease;
}

body {
  font-family: "Segoe UI", Arial, sans-serif;
  background-color: var(--color-light);
  color: var(--color-text);
  line-height: 1.6;
  padding: 40px 20px;
}

.container {
  max-width: 1200px;
  margin: 0 auto;
}

h1 {
  text-align: center;
  color: var(--color-dark);
  margin-bottom: var(--spacing-medium);
}

.subtitle {
  text-align: center;
  color: var(--color-text-light);
  margin-bottom: var(--spacing-xl);
}

/* Demo section */
.section {
  background-color: white;
  border-radius: var(--radius-large);
  padding: var(--spacing-xl);
  margin-bottom: var(--spacing-xl);
  box-shadow: var(--shadow-medium);
}

.section-title {
  font-size: var(--font-large);
  font-weight: bold;
  margin-bottom: var(--spacing-large);
  color: var(--color-dark);
  border-left: 4px solid var(--color-primary);
  padding-left: var(--spacing-medium);
}

.code {
  background-color: #1e1e2e;
  color: #82b1ff;
  padding: var(--spacing-medium);
  border-radius: var(--radius-medium);
  font-family: "Courier New", monospace;
  font-size: 13px;
  overflow-x: auto;
  margin-top: var(--spacing-large);
}

/* ===================================
           DEMO 1: USING VARIABLES FOR COLORS
           =================================== */
.color-demo {
  display: flex;
  gap: var(--spacing-medium);
  flex-wrap: wrap;
  margin: var(--spacing-large) 0;
}

.color-card {
  padding: var(--spacing-large);
  border-radius: var(--radius-medium);
  text-align: center;
  flex: 1;
  min-width: 120px;
  color: white;
}

.color-primary {
  background-color: var(--color-primary);
}
.color-secondary {
  background-color: var(--color-secondary);
}
.color-success {
  background-color: var(--color-success);
}
.color-warning {
  background-color: var(--color-warning);
}
.color-dark {
  background-color: var(--color-dark);
}

/* ===================================
           DEMO 2: BUTTONS WITH VARIABLES
           =================================== */
.btn {
  padding: var(--spacing-small) var(--spacing-large);
  border: none;
  border-radius: var(--radius-medium);
  font-size: var(--font-base);
  cursor: pointer;
  transition: all var(--transition-normal);
  font-weight: bold;
}

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

.btn-primary:hover {
  background-color: #357abd;
  transform: translateY(-2px);
}

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

.btn-secondary:hover {
  background-color: #c73b54;
  transform: translateY(-2px);
}

.btn-outline {
  background-color: transparent;
  border: 2px solid var(--color-primary);
  color: var(--color-primary);
}

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

.button-group {
  display: flex;
  gap: var(--spacing-medium);
  flex-wrap: wrap;
  margin: var(--spacing-large) 0;
}

/* ===================================
           DEMO 3: CARDS WITH VARIABLES
           =================================== */
.card-grid {
  display: flex;
  gap: var(--spacing-large);
  flex-wrap: wrap;
  margin: var(--spacing-large) 0;
}

.card {
  background-color: white;
  border-radius: var(--radius-large);
  padding: var(--spacing-large);
  box-shadow: var(--shadow-small);
  transition: all var(--transition-normal);
  flex: 1;
  min-width: 250px;
  border: 1px solid #eee;
}

.card:hover {
  transform: translateY(-5px);
  box-shadow: var(--shadow-large);
}

.card h3 {
  color: var(--color-primary);
  margin-bottom: var(--spacing-small);
}

.card p {
  color: var(--color-text-light);
  font-size: var(--font-small);
}

/* ===================================
           DEMO 4: THEME SWITCHING
           =================================== */
.theme-demo {
  margin: var(--spacing-large) 0;
}

.theme-buttons {
  display: flex;
  gap: var(--spacing-small);
  margin-bottom: var(--spacing-large);
}

.theme-btn {
  padding: var(--spacing-small) var(--spacing-medium);
  border: none;
  border-radius: var(--radius-small);
  cursor: pointer;
  background-color: var(--color-light);
  border: 1px solid #ddd;
}

.theme-card {
  background-color: white;
  border-radius: var(--radius-medium);
  padding: var(--spacing-large);
  box-shadow: var(--shadow-small);
  transition: all var(--transition-normal);
}

/* Dark theme variables (overrides root) */
.dark-theme {
  --color-primary: #e94560;
  --color-secondary: #4a90e2;
  --color-light: #1a1a2e;
  --color-dark: #f5f5f5;
  --color-text: #eee;
  --color-text-light: #aaa;
  background-color: var(--color-light);
  color: var(--color-text);
}

.dark-theme .theme-card {
  background-color: #16213e;
  color: var(--color-text);
}

/* ===================================
           DEMO 5: SPACING DEMO
           =================================== */
.spacing-demo {
  background-color: var(--color-light);
  border-radius: var(--radius-medium);
  margin: var(--spacing-large) 0;
}

.spacing-box {
  background-color: var(--color-primary);
  color: white;
  text-align: center;
  border-radius: var(--radius-small);
}

.spacing-small {
  padding: var(--spacing-small);
  margin: var(--spacing-small);
}
.spacing-medium {
  padding: var(--spacing-medium);
  margin: var(--spacing-medium);
}
.spacing-large {
  padding: var(--spacing-large);
  margin: var(--spacing-large);
}

/* ===================================
           DEMO 6: BORDER RADIUS DEMO
           =================================== */
.radius-demo {
  display: flex;
  gap: var(--spacing-large);
  flex-wrap: wrap;
  margin: var(--spacing-large) 0;
}

.radius-box {
  width: 100px;
  height: 100px;
  background-color: var(--color-success);
  display: flex;
  align-items: center;
  justify-content: center;
  color: white;
}

.radius-small {
  border-radius: var(--radius-small);
}
.radius-medium {
  border-radius: var(--radius-medium);
}
.radius-large {
  border-radius: var(--radius-large);
}
.radius-circle {
  border-radius: var(--radius-circle);
}

/* ===================================
           DEMO 7: SHADOW DEMO
           =================================== */
.shadow-demo {
  display: flex;
  gap: var(--spacing-large);
  flex-wrap: wrap;
  margin: var(--spacing-large) 0;
}

.shadow-box {
  width: 150px;
  padding: var(--spacing-large);
  background-color: white;
  text-align: center;
  border-radius: var(--radius-medium);
}

.shadow-small {
  box-shadow: var(--shadow-small);
}
.shadow-medium {
  box-shadow: var(--shadow-medium);
}
.shadow-large {
  box-shadow: var(--shadow-large);
}

/* ===================================
           DEMO 8: RESPONSIVE WITH VARIABLES
           =================================== */
.responsive-demo {
  background-color: var(--color-light);
  border-radius: var(--radius-medium);
  padding: var(--spacing-large);
  text-align: center;
}

/* Change variables on smaller screens */
@media (max-width: 768px) {
  .responsive-demo {
    --spacing-large: 16px;
    --font-large: 18px;
    --radius-medium: 8px;
  }
}

footer {
  text-align: center;
  padding: var(--spacing-xl);
  color: var(--color-text-light);
  margin-top: var(--spacing-xl);
}