:root {
    --background: #ffffff;
    --foreground: #1a1a1a;
    --primary: #1a1a1a;
    --secondary: #f5f5f5;
    --border: #e0e0e0;
    --card-bg: #ffffff;
    --card-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
    --success: #1a1a1a;
    --error: #ea2719;
    --warning: #ff9800;
    --info: #1a1a1a;
  }
  
  .dark-theme {
    --background: #121212;
    --foreground: #e0e0e0;
    --primary: #000000;
    --secondary: #1f1f1f;
    --border: #2a2a2a;
    --card-bg: #1a1a1a;
    --card-shadow: 0 2px 6px rgba(0, 0, 0, 0.5);
    --success: #4a645f;
    --error: #9e1010;
    --warning: #7a6430;
    --info: #3c5060;
}
  
  * {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
  }
  
  body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
    background-color: var(--background);
    color: var(--foreground);
    line-height: 1.6;
    transition: background-color 0.3s ease, color 0.3s ease;
  }
  
  header {
    padding: 1rem;
    background-color: var(--card-bg);
    box-shadow: var(--card-shadow);
  }
  
  .header-container {
    max-width: 1200px;
    margin: 0 auto;
    display: flex;
    justify-content: space-between;
    align-items: center;
  }
  
  .theme-toggle button {
    background: none;
    border: none;
    cursor: pointer;
    color: var(--foreground);
    padding: 0.5rem;
    border-radius: 50%;
    transition: background-color 0.3s ease;
  }
  
  .theme-toggle button:hover {
    background-color: var(--secondary);
  }
  
  .container {
    max-width: 1200px;
    margin: 2rem auto;
    padding: 0 1rem;
    display: flex;
    gap: 2rem;
  }
  
  .sidebar {
    width: 250px;
    background-color: var(--card-bg);
    padding: 1rem;
    border-radius: 8px;
    box-shadow: var(--card-shadow);
  }
  
  .categories-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 1rem;
  }
  
  .add-btn {
    background-color: var(--primary);
    color: white;
    border: none;
    border-radius: 50%;
    width: 30px;
    height: 30px;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    transition: background-color 0.3s ease;
  }
  
  .add-btn:disabled {
    background-color: var(--border);
    cursor: not-allowed;
  }
  
  .categories-list {
    list-style: none;
  }
  
  .category-item {
    padding: 0.75rem;
    margin-bottom: 0.5rem;
    border-radius: 4px;
    background-color: var(--secondary);
    cursor: pointer;
    display: flex;
    justify-content: space-between;
    align-items: center;
    transition: background-color 0.3s ease;
  }
  
  .category-item:hover {
    background-color: rgba(var(--primary), 0.1);
  }
  
  .category-item.active {
    background-color: var(--primary);
    color: white;
  }
  
  .category-name {
    flex-grow: 1;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
  }
  
  .category-actions {
    display: flex;
    gap: 0.5rem;
  }
  
  .action-btn {
    background: none;
    border: none;
    cursor: pointer;
    color: inherit;
    padding: 0.25rem;
    border-radius: 4px;
    transition: background-color 0.3s ease;
  }
  
  .action-btn:hover {
    background-color: rgba(0, 0, 0, 0.1);
  }
  
  .flashcards-section {
    flex: 1;
    display: flex;
    flex-direction: column;
  }
  
  .flashcards-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 1rem;
  }
  
  .flashcard-container {
    flex: 1;
    display: flex;
    flex-direction: column;
    gap: 1rem;
  }
  
  .flashcard-display {
    min-height: 300px;
    display: flex;
    justify-content: center;
    align-items: center;
    perspective: 1000px;
  }
  
  .empty-state {
    text-align: center;
    color: var(--foreground);
    opacity: 0.7;
    padding: 2rem;
  }
  
  .flashcard {
    width: 100%;
    max-width: 500px;
    height: 300px;
    position: relative;
    transition: transform 0.6s;
    transform-style: preserve-3d;
    cursor: pointer;
  }
  
  .flashcard.flipped {
    transform: rotateY(180deg);
  }
  
  .flashcard-front, .flashcard-back {
    position: absolute;
    width: 100%;
    height: 100%;
    backface-visibility: hidden;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    padding: 2rem;
    border-radius: 8px;
    box-shadow: var(--card-shadow);
    background-color: var(--card-bg);
    overflow-y: auto;
  }
  
  .flashcard-front {
    z-index: 2;
  }
  
  .flashcard-back {
    transform: rotateY(180deg);
  }
  
  .flashcard-text {
    font-size: 1.25rem;
    text-align: center;
  }
  
  .flashcard-hint {
    margin-top: 1rem;
    font-size: 0.85rem;
    opacity: 0.7;
  }
  
  .navigation-controls {
    display: flex;
    justify-content: center;
    align-items: center;
    gap: 1rem;
    margin-top: 1rem;
  }
  
  .nav-btn {
    background: none;
    border: none;
    cursor: pointer;
    color: var(--foreground);
    padding: 0.5rem;
    border-radius: 50%;
    transition: background-color 0.3s ease;
  }
  
  .nav-btn:hover:not(:disabled) {
    background-color: var(--secondary);
  }
  
  .nav-btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
  }
  
  .card-counter {
    font-size: 0.875rem;
    opacity: 0.7;
  }
  
/* Add the following CSS styles for the CSV upload section */

.csv-section {
  margin-top: 1.5rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--border-color);
}

.csv-help {
  font-size: 0.875rem;
  color: #6b7280;
  margin-bottom: 0.75rem;
}

/* File input styling */
.file-input-container {
  position: relative;
  width: 100%;
  margin-bottom: 0.5rem;
}

.file-input-label {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.75rem 1rem;
  background-color: #f9fafb;
  color: #374151;
  border-radius: 0.375rem;
  cursor: pointer;
  transition: all 0.2s ease;
  border: 1px dashed var(--border-color);
  width: 100%;
  font-size: 0.9rem;
}

.file-input-label:hover {
  background-color: #f3f4f6;
}

.file-input-label svg {
  width: 1.25rem;
  height: 1.25rem;
}

.file-input {
  position: absolute;
  opacity: 0;
  width: 0.1px;
  height: 0.1px;
  overflow: hidden;
}

.file-name {
  margin-left: 0.5rem;
  font-weight: normal;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  max-width: 200px;
}

/* Show the file name when a file is selected */
.file-selected .file-input-label {
  background-color: #e5e7eb;
  border-style: solid;
}

/* Dark theme adjustments */
.dark-theme .file-input-label {
  background-color: #1e293b;
  color: #e2e8f0;
  border-color: #475569;
}

.dark-theme .file-input-label:hover {
  background-color: #2d3748;
}

.dark-theme .file-selected .file-input-label {
  background-color: #334155;
}

.dark-theme .csv-help {
  color: #9ca3af;
}

  /* Modal styles */
  .modal {
    display: none;
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.5);
    z-index: 1000;
    justify-content: center;
    align-items: center;
  }
  
  .modal.active {
    display: flex;
  }
  
  .modal-content {
    background-color: var(--card-bg);
    border-radius: 8px;
    box-shadow: var(--card-shadow);
    width: 90%;
    max-width: 500px;
    max-height: 90vh;
    overflow-y: auto;
  }
  
  .modal-header {
    padding: 1rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
    border-bottom: 1px solid var(--border);
  }
  
  .close-btn {
    background: none;
    border: none;
    cursor: pointer;
    color: var(--foreground);
    padding: 0.25rem;
    border-radius: 50%;
    transition: background-color 0.3s ease;
  }
  
  .close-btn:hover {
    background-color: var(--secondary);
  }
  
  .modal-body {
    padding: 1rem;
  }
  
  .form-group {
    margin-bottom: 1rem;
  }
  
  .form-group label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 500;
  }
  
  input, textarea {
    width: 100%;
    padding: 0.75rem;
    border: 1px solid var(--border);
    border-radius: 4px;
    background-color: var(--background);
    color: var(--foreground);
    font-family: inherit;
    transition: border-color 0.3s ease;
  }
  
  input:focus, textarea:focus {
    outline: none;
    border-color: var(--primary);
  }
  
  textarea {
    min-height: 100px;
    resize: vertical;
  }
  
  .form-actions {
    display: flex;
    justify-content: flex-end;
    gap: 0.5rem;
    margin-top: 1rem;
  }
  
  .cancel-btn, .save-btn, .delete-btn {
    padding: 0.75rem 1rem;
    border: none;
    border-radius: 4px;
    cursor: pointer;
    font-weight: 500;
    transition: background-color 0.3s ease;
  }
  
  .cancel-btn {
    background-color: var(--secondary);
    color: var(--foreground);
  }
  
  .save-btn {
    background-color: var(--primary);
    color: white;
  }
  
  .delete-btn {
    background-color: var(--error);
    color: white;
  }
  

  
  /* Toast notification */
  .toast {
    position: fixed;
    bottom: 20px;
    right: 20px;
    padding: 1rem;
    border-radius: 4px;
    color: white;
    max-width: 300px;
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
    z-index: 1001;
    opacity: 0;
    transform: translateY(20px);
    transition: opacity 0.3s ease, transform 0.3s ease;
  }
  
  .toast.active {
    opacity: 1;
    transform: translateY(0);
  }
  
  .toast.success {
    background-color: var(--success);
  }
  
  .toast.error {
    background-color: var(--error);
  }
  
  .toast.info {
    background-color: var(--info);
  }
  
  /* Responsive design */
  @media (max-width: 768px) {
    .container {
      flex-direction: column;
    }
    
    .sidebar {
      width: 100%;
    }
    
    .flashcard {
      height: 250px;
    }
  }
  
  @media (max-width: 452px) {
    .flashcard-text {
      font-size: 1.0rem !important;
      text-align: center !important;
    }
    html,body h2 {
      font-size: 20px !important;
    }
    html,body h1 {
      font-size: 1.5em;
    }

    .category-name {
      flex-grow: 1;
      white-space: nowrap;
      overflow: hidden;
      text-overflow: ellipsis;
      font-size: 16px;
  }
  }