:root {
  --bg-color: #f0f7ff;
  --text-color: #333;
  --header-color: #2563eb;
  --card-bg: #fff;
  --card-shadow: rgba(0, 0, 0, 0.08);
  --footer-text: #6c757d;
  --button-color: #2563eb;
  --button-hover-color: #1d4ed8;
}

body.dark-mode {
  --bg-color: #1a202c;
  --text-color: #e2e8f0;
  --header-color: #60a5fa;
  --card-bg: #2d3748;
  --card-shadow: rgba(0, 0, 0, 0.4);
  --footer-text: #a0aec0;
  --button-color: #60a5fa;
  --button-hover-color: #3b82f6;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
  background-color: var(--bg-color);
  color: var(--text-color);
  line-height: 1.6;
  margin: 0;
  transition: background-color 0.3s, color 0.3s;
}

.page-container {
  display: flex;
  flex-direction: column;
  min-height: 100vh;
}

.main-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  background: var(--bg-color);
  padding: 15px 30px;
  margin-bottom: 30px;
  box-shadow: 0 2px 5px var(--card-shadow);
}

.title-container {
  text-align: center;
  flex-grow: 1;
}

.title-container h1 {
  font-size: 2.2em;
  color: var(--header-color);
  margin: 0;
  font-weight: 700;
}

.subtitle {
  margin: 0;
  color: var(--text-color);
  opacity: 0.8;
}

.theme-btn {
  background: none;
  border: none;
  font-size: 1.5em;
  cursor: pointer;
}

.home-content {
  flex: 1;
  max-width: 1200px;
  width: 100%;
  margin: 0 auto;
  padding: 0 20px;
  box-sizing: border-box;
}

.intro-text {
  text-align: center;
  font-size: 1.2em;
  margin-bottom: 40px;
}

.chapter-cards-container {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 30px;
}

.chapter-card {
  background: var(--card-bg);
  border-radius: 12px;
  box-shadow: 0 4px 12px var(--card-shadow);
  display: flex;
  flex-direction: column;
  transition: transform 0.2s, box-shadow 0.2s;
}

.chapter-card:hover {
  transform: translateY(-5px);
  box-shadow: 0 8px 20px var(--card-shadow);
}

.card-content {
  padding: 30px;
  display: flex;
  flex-direction: column;
  flex-grow: 1;
}

.card-content h2 {
  color: var(--header-color);
  margin-top: 0;
  font-size: 1.4em;
}

.card-content p {
  flex-grow: 1;
  margin-bottom: 30px;
}

.cta-button {
  display: inline-block;
  background-color: var(--button-color);
  color: white;
  text-align: center;
  padding: 12px 20px;
  border-radius: 8px;
  text-decoration: none;
  font-weight: bold;
  transition: background-color 0.2s;
  align-self: flex-start;
}

.cta-button:hover {
  background-color: var(--button-hover-color);
}

footer {
  text-align: center;
  padding: 20px;
  margin-top: auto;
  color: var(--footer-text);
  font-size: 0.9em;
}

/* Responsive Design for Homepage */
@media (max-width: 768px) {
  .chapter-cards-container {
    grid-template-columns: 1fr;
  }
  .title-container h1 {
    font-size: 1.8em;
  }
}