:root {
    /* Light Mode Colors */
    --bg-primary: #f0f4f8;
    --bg-secondary: #ffffff;
    --bg-glass: rgba(255, 255, 255, 0.7);
    --text-primary: #1a202c;
    --text-secondary: #4a5568;
    --text-muted: #718096;
    --border-color: rgba(226, 232, 240, 0.8);
    --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.04);
    --shadow-md: 0 4px 16px rgba(0, 0, 0, 0.08);
    --shadow-lg: 0 8px 32px rgba(0, 0, 0, 0.12);
    --accent-primary: #667eea;
    --accent-secondary: #764ba2;
    --success: #48bb78;
    --warning: #ed8936;
    --danger: #f56565;
    
    /* Priority Colors */
    --priority-low: #48bb78;
    --priority-medium: #ed8936;
    --priority-high: #f56565;
}

[data-theme="dark"] {
    --bg-primary: #0f1419;
    --bg-secondary: #1a1f2e;
    --bg-glass: rgba(26, 31, 46, 0.7);
    --text-primary: #e2e8f0;
    --text-secondary: #cbd5e0;
    --text-muted: #a0aec0;
    --border-color: rgba(74, 85, 104, 0.3);
    --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.3);
    --shadow-md: 0 4px 16px rgba(0, 0, 0, 0.4);
    --shadow-lg: 0 8px 32px rgba(0, 0, 0, 0.5);
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    background: var(--bg-primary);
    color: var(--text-primary);
    line-height: 1.6;
    transition: background-color 0.3s ease, color 0.3s ease;
    min-height: 100vh;
    background-image: 
        radial-gradient(circle at 20% 50%, rgba(102, 126, 234, 0.1) 0%, transparent 50%),
        radial-gradient(circle at 80% 80%, rgba(118, 75, 162, 0.1) 0%, transparent 50%);
    background-attachment: fixed;
}

.container {
    max-width: 1400px;
    margin: 0 auto;
    padding: 2rem;
}

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

.header-content {
    display: flex;
    justify-content: space-between;
    align-items: center;
    background: var(--bg-glass);
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    padding: 1.5rem 2rem;
    border-radius: 20px;
    border: 1px solid var(--border-color);
    box-shadow: var(--shadow-md);
}

.logo {
    font-size: 1.8rem;
    font-weight: 700;
    background: linear-gradient(135deg, var(--accent-primary), var(--accent-secondary));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.logo-icon {
    font-size: 2rem;
}

/* Theme Toggle */
.theme-toggle {
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: 50px;
    width: 60px;
    height: 32px;
    cursor: pointer;
    position: relative;
    transition: all 0.3s ease;
    display: flex;
    align-items: center;
    padding: 0 4px;
}

.theme-toggle:hover {
    transform: scale(1.05);
    box-shadow: var(--shadow-sm);
}

.theme-toggle span {
    font-size: 1rem;
    position: absolute;
    transition: all 0.3s ease;
}

.sun-icon {
    left: 8px;
    opacity: 1;
}

.moon-icon {
    right: 8px;
    opacity: 0;
}

[data-theme="dark"] .sun-icon {
    opacity: 0;
}

[data-theme="dark"] .moon-icon {
    opacity: 1;
}

/* Stats Grid */
.stats-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 1.5rem;
    margin-bottom: 2rem;
}

.stat-card {
    background: var(--bg-glass);
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    padding: 1.5rem;
    border-radius: 16px;
    border: 1px solid var(--border-color);
    box-shadow: var(--shadow-sm);
    display: flex;
    align-items: center;
    gap: 1rem;
    transition: all 0.3s ease;
}

.stat-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-md);
}

.stat-icon {
    font-size: 2.5rem;
    width: 60px;
    height: 60px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: linear-gradient(135deg, var(--accent-primary), var(--accent-secondary));
    border-radius: 12px;
    opacity: 0.9;
}

.stat-content {
    flex: 1;
}

.stat-value {
    font-size: 2rem;
    font-weight: 700;
    color: var(--text-primary);
    line-height: 1;
    margin-bottom: 0.25rem;
}

.stat-label {
    font-size: 0.875rem;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

/* Add Section */
.add-task-section {
    margin-bottom: 2rem;
}

.add-task-card {
    background: var(--bg-glass);
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    padding: 2rem;
    border-radius: 20px;
    border: 1px solid var(--border-color);
    box-shadow: var(--shadow-md);
}

.section-title {
    font-size: 1.5rem;
    font-weight: 600;
    margin-bottom: 1.5rem;
    color: var(--text-primary);
}

.add-task-form {
    display: flex;
    flex-direction: column;
    gap: 1rem;
}

.form-row {
    display: grid;
    grid-template-columns: 1fr auto;
    gap: 1rem;
}

.form-input,
.form-select {
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: 12px;
    padding: 0.875rem 1.25rem;
    font-size: 1rem;
    color: var(--text-primary);
    transition: all 0.3s ease;
    font-family: inherit;
}

.form-input:focus,
.form-select:focus {
    outline: none;
    border-color: var(--accent-primary);
    box-shadow: 0 0 0 3px rgba(102, 126, 234, 0.1);
}

.form-select {
    min-width: 200px;
    cursor: pointer;
}

.btn-primary {
    background: linear-gradient(135deg, var(--accent-primary), var(--accent-secondary));
    color: white;
    border: none;
    border-radius: 12px;
    padding: 1rem 2rem;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    transition: all 0.3s ease;
    box-shadow: 0 4px 12px rgba(102, 126, 234, 0.3);
}

.btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(102, 126, 234, 0.4);
}

.btn-primary:active {
    transform: translateY(0);
}

.btn-icon {
    font-size: 1.5rem;
    line-height: 1;
}

/* Tasks Section */
.tasks-columns {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
    gap: 1.5rem;
}

.task-column {
    background: var(--bg-glass);
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    border-radius: 20px;
    border: 1px solid var(--border-color);
    padding: 1.5rem;
    box-shadow: var(--shadow-sm);
}

.column-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 1.5rem;
    padding-bottom: 1rem;
    border-bottom: 2px solid var(--border-color);
}

.column-title {
    font-size: 1.125rem;
    font-weight: 600;
    display: flex;
    align-items: center;
    gap: 0.5rem;
    color: var(--text-primary);
}

.column-icon {
    font-size: 1.5rem;
}

.task-count {
    background: var(--accent-primary);
    color: white;
    padding: 0.25rem 0.75rem;
    border-radius: 20px;
    font-size: 0.875rem;
    font-weight: 600;
}

.task-list {
    display: flex;
    flex-direction: column;
    gap: 1rem;
    min-height: 200px;
}

.task-list.drag-over {
    background: rgba(102, 126, 234, 0.05);
    border-radius: 12px;
}

/* Task Card */
.task-card {
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: 12px;
    padding: 1.25rem;
    box-shadow: var(--shadow-sm);
    cursor: grab;
    transition: all 0.3s ease;
    position: relative;
    overflow: hidden;
}

.task-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 4px;
    height: 100%;
    background: var(--priority-color);
}

.task-card.priority-low {
    --priority-color: var(--priority-low);
}

.task-card.priority-medium {
    --priority-color: var(--priority-medium);
}

.task-card.priority-high {
    --priority-color: var(--priority-high);
}

.task-card:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

.task-card.dragging {
    opacity: 0.5;
    cursor: grabbing;
}

.task-header {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    margin-bottom: 0.75rem;
}

.task-title {
    font-size: 1rem;
    font-weight: 600;
    color: var(--text-primary);
    flex: 1;
    word-wrap: break-word;
}

.task-actions {
    display: flex;
    gap: 0.5rem;
}

.task-btn {
    background: transparent;
    border: none;
    cursor: pointer;
    font-size: 1.25rem;
    opacity: 0.6;
    transition: all 0.2s ease;
    padding: 0.25rem;
}

.task-btn:hover {
    opacity: 1;
    transform: scale(1.1);
}

.task-meta {
    display: flex;
    gap: 0.75rem;
    align-items: center;
}

.task-priority {
    display: inline-flex;
    align-items: center;
    gap: 0.25rem;
    padding: 0.25rem 0.75rem;
    border-radius: 20px;
    font-size: 0.75rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.task-priority.low {
    background: rgba(72, 187, 120, 0.1);
    color: var(--priority-low);
}

.task-priority.medium {
    background: rgba(237, 137, 54, 0.1);
    color: var(--priority-medium);
}

.task-priority.high {
    background: rgba(245, 101, 101, 0.1);
    color: var(--priority-high);
}

.task-time {
    font-size: 0.75rem;
    color: var(--text-muted);
}

/* Empty State */
.empty-state {
    text-align: center;
    padding: 3rem 1rem;
    color: var(--text-muted);
}

.empty-state-icon {
    font-size: 4rem;
    margin-bottom: 1rem;
    opacity: 0.5;
}

.empty-state-text {
    font-size: 0.875rem;
}

/* Animations */
@keyframes slideIn {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.task-card {
    animation: slideIn 0.3s ease;
}

@keyframes pulse {
    0%, 100% {
        opacity: 1;
    }
    50% {
        opacity: 0.5;
    }
}

.task-card.pulse {
    animation: pulse 0.5s ease;
}

/* Responsive Design */
@media (max-width: 1024px) {
    .tasks-columns {
        grid-template-columns: 1fr;
    }
}

@media (max-width: 768px) {
    .container {
        padding: 1rem;
    }
    
    .header-content {
        padding: 1rem 1.5rem;
    }
    
    .logo {
        font-size: 1.5rem;
    }
    
    .stats-grid {
        grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
        gap: 1rem;
    }
    
    .stat-card {
        padding: 1rem;
    }
    
    .stat-icon {
        width: 50px;
        height: 50px;
        font-size: 2rem;
    }
    
    .stat-value {
        font-size: 1.5rem;
    }
    
    .form-row {
        grid-template-columns: 1fr;
    }
    
    .add-task-card {
        padding: 1.5rem;
    }
    
    .task-column {
        padding: 1rem;
    }
}

@media (max-width: 480px) {
    .stats-grid {
        grid-template-columns: 1fr;
    }
    
    .section-title {
        font-size: 1.25rem;
    }
    
    .form-select {
        min-width: 100%;
    }
}