/*
  DARK MODE TOGGLE - STYLES

  This stylesheet demonstrates:
  - CSS Custom Properties (CSS Variables)
  - Theme switching using a single class
  - Smooth transitions between themes
  - Responsive design principles
*/

/* ===================================
   CSS VARIABLES (CUSTOM PROPERTIES)
   ===================================
   We define color schemes using CSS variables.
   The :root selector defines variables for LIGHT MODE (default).
*/

:root {
  /* Light mode colors */
  --bg-primary: #ffffff;
  --bg-secondary: #f8f9fa;
  --bg-card: #ffffff;
  --text-primary: #2c3e50;
  --text-secondary: #5a6c7d;
  --border-color: #e1e4e8;
  --accent-color: #4a90e2;
  --shadow: rgba(0, 0, 0, 0.1);

  /* Spacing */
  --spacing-sm: 1rem;
  --spacing-md: 1.5rem;
  --spacing-lg: 2rem;
  --spacing-xl: 3rem;

  /* Font */
  --font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
}

/*
  DARK MODE VARIABLES
  When the body has class "dark-mode", these variables override the defaults.
  We only need to change the colors - all other CSS stays the same!
*/

body.dark-mode {
  --bg-primary: #1a1a1a;
  --bg-secondary: #2d2d2d;
  --bg-card: #252525;
  --text-primary: #e8e8e8;
  --text-secondary: #b0b0b0;
  --border-color: #404040;
  --accent-color: #5ca3f5;
  --shadow: rgba(0, 0, 0, 0.5);
}

/* ===================================
   BASE STYLES
   ===================================
   These styles use our CSS variables, so they automatically
   adapt when we switch between light and dark mode.
*/

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

body {
  font-family: var(--font-family);
  background-color: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.6;
  /*
    IMPORTANT: Add transition for smooth theme switching.
    This animates all color changes when toggling dark mode.
  */
  transition: background-color 0.3s ease, color 0.3s ease;
}

/* ===================================
   CONTAINER & LAYOUT
   =================================== */

.container {
  max-width: 900px;
  margin: 0 auto;
  padding: var(--spacing-md);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

main {
  flex: 1; /* Main content takes up available space */
}

/* ===================================
   HEADER & THEME TOGGLE BUTTON
   =================================== */

header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: var(--spacing-md) 0;
  border-bottom: 2px solid var(--border-color);
  margin-bottom: var(--spacing-lg);
}

header h1 {
  font-size: 2rem;
  color: var(--text-primary);
}

/*
  THEME TOGGLE BUTTON
  This button switches between sun and moon icons
*/

.theme-toggle {
  background-color: var(--bg-card);
  border: 2px solid var(--border-color);
  border-radius: 50%; /* Makes it circular */
  width: 50px;
  height: 50px;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.5rem;
  transition: all 0.3s ease;
  position: relative;
}

.theme-toggle:hover {
  transform: scale(1.1); /* Slightly larger on hover */
  border-color: var(--accent-color);
}

.theme-toggle:active {
  transform: scale(0.95); /* Slightly smaller when clicked */
}

/*
  ICON VISIBILITY
  We show moon icon in light mode, sun icon in dark mode
*/

.icon {
  position: absolute;
  transition: opacity 0.3s ease, transform 0.3s ease;
}

/* Light mode: Show moon, hide sun */
.icon-moon {
  opacity: 1;
  transform: rotate(0deg);
}

.icon-sun {
  opacity: 0;
  transform: rotate(180deg);
}

/* Dark mode: Hide moon, show sun */
body.dark-mode .icon-moon {
  opacity: 0;
  transform: rotate(-180deg);
}

body.dark-mode .icon-sun {
  opacity: 1;
  transform: rotate(0deg);
}

/* ===================================
   CONTENT SECTIONS
   =================================== */

section {
  margin-bottom: var(--spacing-xl);
}

h2 {
  font-size: 1.75rem;
  margin-bottom: var(--spacing-md);
  color: var(--accent-color);
}

h3 {
  font-size: 1.25rem;
  margin-bottom: var(--spacing-sm);
  color: var(--text-primary);
}

p {
  color: var(--text-secondary);
  margin-bottom: var(--spacing-sm);
  line-height: 1.7;
}

/* ===================================
   CARDS
   =================================== */

.features {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
  gap: var(--spacing-md);
}

.card {
  background-color: var(--bg-card);
  border: 1px solid var(--border-color);
  border-radius: 8px;
  padding: var(--spacing-md);
  transition: all 0.3s ease;
  /* Add shadow for depth */
  box-shadow: 0 2px 8px var(--shadow);
}

.card:hover {
  transform: translateY(-4px); /* Lift up on hover */
  box-shadow: 0 4px 16px var(--shadow);
  border-color: var(--accent-color);
}

/* ===================================
   BLOCKQUOTE
   =================================== */

blockquote {
  background-color: var(--bg-secondary);
  border-left: 4px solid var(--accent-color);
  padding: var(--spacing-md);
  margin: var(--spacing-lg) 0;
  font-style: italic;
  color: var(--text-secondary);
  border-radius: 4px;
}

blockquote footer {
  margin-top: var(--spacing-sm);
  font-size: 0.9rem;
  color: var(--text-primary);
  font-style: normal;
}

/* ===================================
   FOOTER
   =================================== */

footer {
  text-align: center;
  padding: var(--spacing-lg) 0;
  border-top: 2px solid var(--border-color);
  margin-top: var(--spacing-xl);
  color: var(--text-secondary);
}

footer a {
  color: var(--accent-color);
  text-decoration: none;
  border-bottom: 1px solid transparent;
  transition: border-color 0.2s ease;
}

footer a:hover {
  border-bottom-color: var(--accent-color);
}

/* ===================================
   RESPONSIVE DESIGN
   =================================== */

@media (max-width: 768px) {
  header h1 {
    font-size: 1.5rem;
  }

  .features {
    grid-template-columns: 1fr; /* Stack cards on mobile */
  }
}