/* --- 1. Base Variables & Reset --- */
  :root {
    --bg-color: #f9fafb;
    --card-bg: #ffffff;
    --text-main: #111827;
    --text-sub: #4b5563;
    --accent: #2563eb;
    --radius: 12px;
    --shadow: 0 4px 6px -1px rgba(0,0,0,0.1);
  }

  body {
    font-family: system-ui, -apple-system, sans-serif;
    background: var(--bg-color);
    color: var(--text-main);
    margin: 0;
    padding: 1.5rem 1rem;
    line-height: 1.6;
  }

  /* --- 2. Header  --- */
  header {
    margin-bottom: 2rem;
    text-align: center;
  }

  h1 {
    font-size: 2rem;
    margin-bottom: 0.5rem;
    color: var(--text-main);
  }

  /* --- 3. The Book List (Vertical Stack) --- */
  .book-list {
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
    max-width: 800px;
    margin: 0 auto;
  }

  /* --- 4. The Book Card --- */
  .book-card {
    display: flex;
    flex-direction: column; /* Mobile First: Stacked */
    background: var(--card-bg);
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    overflow: hidden;
    transition: transform 0.2s;
  }

  .book-card:hover {
    transform: translateY(-3px);
    box-shadow: 0 10px 15px -3px rgba(0,0,0,0.1);
  }

  /* Image Container */
  .book-cover {
    width: 100%;
    height: 200px; /* Fixed height for consistency */
    object-fit: cover;
    background: #e5e7eb; /* Placeholder color */
  }

  .book-content {
    padding: 1.5rem;
    display: flex;
    flex-direction: column;
    flex: 1;
  }

  .book-title {
    font-size: 1.25rem;
    font-weight: 700;
    margin: 0 0 0.5rem 0;
    color: var(--text-main);
  }

  .book-meta {
    font-size: 0.85rem;
    color: var(--text-sub);
    margin-bottom: 0.75rem;
    font-style: italic;
  }

  .book-desc {
    font-size: 1rem;
    color: var(--text-sub);
    margin-bottom: 1.25rem;
    flex: 1; /* Pushes button down */
  }

  .book-btn {
    display: inline-block;
    background: var(--accent);
    color: white;
    padding: 0.75rem 1.5rem;
    border-radius: 8px;
    text-decoration: none;
    font-weight: 600;
    text-align: center;
    transition: background 0.2s;
    align-self: flex-start;
  }

  .book-btn:hover {
    background: #1d4ed8;
  }

  /* --- 5. Desktop Layout (Row) --- */
  @media (min-width: 600px) {
    .book-card {
      flex-direction: row; /* Side-by-side on desktop */
      height: auto;
    }

    .book-cover {
      width: 200px;
      height: 100%;
      min-height: 250px;
    }

    .book-content {
      padding: 2rem;
    }

    .book-btn {
      align-self: flex-start;
    }
  }