/* CSS Variables for Light & Dark Themes */
:root {
    --bg-color: #f4f6f9;
    --card-bg: #ffffff;
    --text-primary: #1f2937;
    --text-secondary: #4b5563;
    --border-color: #e5e7eb;
    --primary-color: #2563eb;
    --primary-hover: #1d4ed8;
    --accent-color: #10b981;
    --danger-color: #ef4444;
    --shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
  }
  
  [data-theme="dark"] {
    --bg-color: #111827;
    --card-bg: #1f2937;
    --text-primary: #f9fafb;
    --text-secondary: #9ca3af;
    --border-color: #374151;
    --primary-color: #3b82f6;
    --primary-hover: #60a5fa;
    --accent-color: #34d399;
    --danger-color: #f87171;
    --shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.5);
  }
  
  /* Global Styles */
  * {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  }
  
  body {
    background-color: var(--bg-color);
    color: var(--text-primary);
    line-height: 1.6;
    padding: 1rem;
    transition: background-color 0.3s ease, color 0.3s ease;
  }
  
  header {
    max-width: 700px;
    margin: 0 auto 1.5rem auto;
    padding: 1rem;
    background: var(--card-bg);
    border-radius: 12px;
    box-shadow: var(--shadow);
    border: 1px solid var(--border-color);
  }
  
  .header-top {
    display: flex;
    justify-content: space-between;
    align-items: center;
  }
  
  header h1 {
    font-size: 1.5rem;
    color: var(--text-primary);
  }
  
  .subtitle {
    font-size: 0.85rem;
    color: var(--text-secondary);
    margin-top: 0.25rem;
  }
  
  /* Header Control Buttons */
  .app-controls {
    display: flex;
    gap: 0.5rem;
  }
  
  .control-btn {
    background: var(--bg-color);
    border: 1px solid var(--border-color);
    color: var(--text-primary);
    padding: 0.4rem 0.7rem;
    border-radius: 8px;
    font-size: 0.8rem;
    cursor: pointer;
    font-weight: 600;
    transition: all 0.2s;
  }
  
  .control-btn:hover {
    background: var(--border-color);
  }
  
  /* Main Container & Tabs */
  main {
    max-width: 700px;
    margin: 0 auto;
  }
  
  .tab-bar {
    display: flex;
    gap: 0.5rem;
    margin-bottom: 1rem;
  }
  
  .tab-btn {
    flex: 1;
    padding: 0.75rem;
    background: var(--card-bg);
    border: 1px solid var(--border-color);
    color: var(--text-secondary);
    font-size: 1rem;
    font-weight: bold;
    border-radius: 10px;
    cursor: pointer;
    transition: all 0.2s;
  }
  
  .tab-btn.active {
    background: var(--primary-color);
    color: white;
    border-color: var(--primary-color);
  }
  
  /* Cards */
  .card {
    background: var(--card-bg);
    border: 1px solid var(--border-color);
    border-radius: 12px;
    padding: 1.5rem;
    margin-bottom: 1rem;
    box-shadow: var(--shadow);
  }
  
  .card h2 {
    font-size: 1.2rem;
    margin-bottom: 1rem;
    color: var(--text-primary);
  }
  
  /* Forms */
  .form-group {
    margin-bottom: 1rem;
  }
  
  .form-group label {
    display: block;
    font-size: 0.9rem;
    font-weight: 600;
    margin-bottom: 0.4rem;
    color: var(--text-secondary);
  }
  
  .form-group input,
  .form-group select {
    width: 100%;
    padding: 0.75rem;
    border: 1px solid var(--border-color);
    border-radius: 8px;
    background: var(--bg-color);
    color: var(--text-primary);
    font-size: 1rem;
  }
  
  .form-group input:focus,
  .form-group select:focus {
    outline: none;
    border-color: var(--primary-color);
  }
  
  /* Buttons */
  .btn {
    display: inline-block;
    width: 100%;
    padding: 0.75rem;
    border: none;
    border-radius: 8px;
    font-size: 1rem;
    font-weight: bold;
    cursor: pointer;
    text-align: center;
    transition: background 0.2s;
  }
  
  .btn.primary {
    background: var(--primary-color);
    color: white;
  }
  
  .btn.primary:hover {
    background: var(--primary-hover);
  }
  
  /* Utility Classes */
  .hidden {
    display: none !important;
  }