:root {
            --primary: #3498db;
            --secondary: #2ecc71;
            --danger: #e74c3c;
            --warning: #f39c12;
            --light: #ecf0f1;
            --dark: #34495e;
            --shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
            
            /* Light Theme Colors (Default) */
            --bg-color: #f5f7fa;
            --text-color: #333;
            --card-bg: #ffffff;
            --border-color: #ddd;
            --header-bg: #3498db;
            --header-text: #ffffff;
            --task-bg: #ecf0f1;
            --dropzone-border: #ddd;
            --dropzone-text: #999;
        }
        
        [data-theme="dark"] {
            /* Dark Theme Colors */
            --bg-color: #1a1a2e;
            --text-color: #e6e6e6;
            --card-bg: #16213e;
            --border-color: #2c3e50;
            --header-bg: #1e3a8a;
            --header-text: #ffffff;
            --task-bg: #24283b;
            --dropzone-border: #2c3e50;
            --dropzone-text: #8f9aab;
            --shadow: 0 4px 6px rgba(0, 0, 0, 0.3);
        }
        
        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
            transition: background-color 0.3s ease, color 0.3s ease;
        }
        
        body {
            background-color: var(--bg-color);
            color: var(--text-color);
            line-height: 1.6;
        }
        
        header {
            background-color: var(--header-bg);
            color: var(--header-text);
            text-align: center;
            padding: 1.5rem;
            box-shadow: var(--shadow);
            position: relative;
        }
        
        .theme-toggle {
            position: absolute;
            top: 1.5rem;
            right: 1.5rem;
            background: transparent;
            border: 2px solid var(--header-text);
            color: var(--header-text);
            border-radius: 50%;
            width: 40px;
            height: 40px;
            display: flex;
            align-items: center;
            justify-content: center;
            cursor: pointer;
            transition: all 0.3s ease;
        }
        
        .theme-toggle:hover {
            background-color: rgba(255, 255, 255, 0.2);
        }
        
        .theme-toggle i {
            font-size: 1.2rem;
        }
        
        .container {
            width: 95%;
            max-width: 1200px;
            margin: 2rem auto;
        }
        
        .controls {
            display: flex;
            justify-content: space-between;
            margin-bottom: 1.5rem;
            flex-wrap: wrap;
            gap: 1rem;
        }
        
        .task-form {
            display: flex;
            flex-wrap: wrap;
            gap: 0.5rem;
            margin-bottom: 1rem;
            width: 100%;
        }
        
        .task-input {
            flex: 1;
            padding: 0.8rem;
            border: 1px solid var(--border-color);
            border-radius: 4px;
            font-size: 1rem;
            background-color: var(--card-bg);
            color: var(--text-color);
        }
        
        .select-input {
            padding: 0.8rem;
            border: 1px solid var(--border-color);
            border-radius: 4px;
            background-color: var(--card-bg);
            color: var(--text-color);
            min-width: 120px;
        }
        
        .btn {
            padding: 0.8rem 1.2rem;
            border: none;
            border-radius: 4px;
            cursor: pointer;
            font-weight: bold;
            transition: all 0.3s ease;
        }
        
        .btn-primary {
            background-color: var(--primary);
            color: white;
        }
        
        .btn-primary:hover {
            background-color: #2980b9;
        }
        
        .btn-danger {
            background-color: var(--danger);
            color: white;
        }
        
        .btn-danger:hover {
            background-color: #c0392b;
        }
        
        .board {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
            gap: 1.5rem;
        }
        
        .category {
            background-color: var(--card-bg);
            border-radius: 8px;
            box-shadow: var(--shadow);
            padding: 1rem;
            min-height: 400px;
        }
        
        .category-header {
            display: flex;
            justify-content: space-between;
            align-items: center;
            padding-bottom: 1rem;
            border-bottom: 2px solid #eee;
            margin-bottom: 1rem;
        }
        
        .category-name {
            font-size: 1.2rem;
            font-weight: bold;
            color: var(--dark);
        }
        
        .task-count {
            background-color: var(--light);
            color: var(--dark);
            padding: 0.25rem 0.5rem;
            border-radius: 20px;
            font-size: 0.9rem;
        }
        
        .task-list {
            min-height: 300px;
        }
        
        .task {
            background-color: var(--task-bg);
            padding: 1rem;
            border-radius: 4px;
            margin-bottom: 0.8rem;
            cursor: grab;
            position: relative;
            border-left: 4px solid var(--primary);
            transition: all 0.2s ease;
        }
        
        .task:hover {
            box-shadow: var(--shadow);
        }
        
        .task-dragging {
            opacity: 0.7;
        }
        
        .task-header {
            display: flex;
            justify-content: space-between;
            margin-bottom: 0.5rem;
        }
        
        .task-priority {
            font-size: 0.8rem;
            padding: 0.2rem 0.4rem;
            border-radius: 3px;
            color: white;
        }
        
        .priority-high {
            background-color: var(--danger);
        }
        
        .priority-medium {
            background-color: var(--warning);
        }
        
        .priority-low {
            background-color: var(--secondary);
        }
        
        .task-actions {
            display: flex;
            gap: 0.5rem;
        }
        
        .task-btn {
            background: none;
            border: none;
            cursor: pointer;
            font-size: 0.9rem;
            opacity: 0.7;
            transition: opacity 0.2s;
        }
        
        .task-btn:hover {
            opacity: 1;
        }
        
        .task-complete {
            text-decoration: line-through;
            opacity: 0.6;
        }
        
        .dropzone {
            min-height: 100px;
            border: 2px dashed var(--dropzone-border);
            border-radius: 4px;
            display: flex;
            justify-content: center;
            align-items: center;
            margin: 1rem 0;
            color: var(--dropzone-text);
        }
        
        .dragover {
            background-color: rgba(46, 204, 113, 0.1);
            border-color: var(--secondary);
        }
        
        @media (max-width: 768px) {
            .controls {
                flex-direction: column;
            }
            
            .board {
                grid-template-columns: 1fr;
            }
        }