/* CSS Reset and Base Styles */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root {
    /* Light Theme Colors */
    --bg-primary: #ffffff;
    --bg-secondary: #f8fafc;
    --bg-tertiary: #f1f5f9;
    --text-primary: #1e293b;
    --text-secondary: #64748b;
    --text-muted: #94a3b8;
    --accent-primary: #3b82f6;
    --accent-secondary: #1d4ed8;
    --success: #10b981;
    --danger: #ef4444;
    --warning: #f59e0b;
    --border: #e2e8f0;
    --shadow: rgba(0, 0, 0, 0.1);
    --shadow-lg: rgba(0, 0, 0, 0.15);
    
    /* Spacing */
    --spacing-xs: 0.25rem;
    --spacing-sm: 0.5rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-2xl: 3rem;
    
    /* Border Radius */
    --radius-sm: 0.375rem;
    --radius-md: 0.5rem;
    --radius-lg: 0.75rem;
    --radius-xl: 1rem;
    
    /* Transitions */
    --transition: all 0.2s ease-in-out;
    --transition-slow: all 0.3s ease-in-out;
}

[data-theme="dark"] {
    --bg-primary: #0f172a;
    --bg-secondary: #1e293b;
    --bg-tertiary: #334155;
    --text-primary: #f1f5f9;
    --text-secondary: #cbd5e1;
    --text-muted: #94a3b8;
    --accent-primary: #3b82f6;
    --accent-secondary: #60a5fa;
    --border: #334155;
    --shadow: rgba(0, 0, 0, 0.3);
    --shadow-lg: rgba(0, 0, 0, 0.4);
}

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background: linear-gradient(135deg, var(--bg-secondary) 0%, var(--bg-tertiary) 100%);
    color: var(--text-primary);
    line-height: 1.6;
    min-height: 100vh;
    transition: var(--transition);
}

.container {
    max-width: 600px;
    margin: 0 auto;
    padding: var(--spacing-md);
    min-height: 100vh;
}

/* Header Styles */
.header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: var(--spacing-lg) 0;
    margin-bottom: var(--spacing-xl);
}

.logo {
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
}

.logo-icon {
    width: 48px;
    height: 48px;
    background: linear-gradient(135deg, var(--accent-primary), var(--accent-secondary));
    border-radius: var(--radius-lg);
    display: flex;
    align-items: center;
    justify-content: center;
    color: white;
    font-size: 1.5rem;
    font-weight: 700;
    box-shadow: 0 4px 12px var(--shadow);
}

.logo h1 {
    font-size: 2rem;
    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;
}

.theme-toggle {
    width: 48px;
    height: 48px;
    border: none;
    background: var(--bg-primary);
    border-radius: var(--radius-lg);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.25rem;
    transition: var(--transition);
    box-shadow: 0 2px 8px var(--shadow);
    border: 1px solid var(--border);
}

.theme-toggle:hover {
    transform: translateY(-2px);
    box-shadow: 0 4px 12px var(--shadow-lg);
}

/* App Styles */
.app {
    background: var(--bg-primary);
    border-radius: var(--radius-xl);
    padding: var(--spacing-xl);
    box-shadow: 0 8px 32px var(--shadow-lg);
    border: 1px solid var(--border);
}

/* Input Section */
.input-section {
    margin-bottom: var(--spacing-xl);
}

.input-container {
    display: flex;
    gap: var(--spacing-md);
    flex-wrap: wrap;
}

#taskInput {
    flex: 1;
    min-width: 250px;
    padding: var(--spacing-md) var(--spacing-lg);
    border: 2px solid var(--border);
    border-radius: var(--radius-lg);
    font-size: 1rem;
    background: var(--bg-secondary);
    color: var(--text-primary);
    transition: var(--transition);
    outline: none;
}

#taskInput:focus {
    border-color: var(--accent-primary);
    box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.1);
}

#taskInput::placeholder {
    color: var(--text-muted);
}

.add-btn {
    padding: var(--spacing-md) var(--spacing-lg);
    background: linear-gradient(135deg, var(--accent-primary), var(--accent-secondary));
    color: white;
    border: none;
    border-radius: var(--radius-lg);
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: var(--transition);
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    white-space: nowrap;
}

.add-btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(59, 130, 246, 0.3);
}

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

.add-icon {
    font-size: 1.25rem;
    font-weight: 300;
}

/* Stats Section */
.stats-section {
    margin-bottom: var(--spacing-xl);
}

.stats {
    display: flex;
    justify-content: space-around;
    background: var(--bg-secondary);
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    border: 1px solid var(--border);
}

.stat-item {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: var(--spacing-xs);
}

.stat-number {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--accent-primary);
}

.stat-label {
    font-size: 0.875rem;
    color: var(--text-secondary);
    font-weight: 500;
}

/* Filter Section */
.filter-section {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: var(--spacing-xl);
    flex-wrap: wrap;
    gap: var(--spacing-md);
}

.filters {
    display: flex;
    gap: var(--spacing-xs);
    background: var(--bg-secondary);
    padding: var(--spacing-xs);
    border-radius: var(--radius-lg);
    border: 1px solid var(--border);
}

.filter-btn {
    padding: var(--spacing-sm) var(--spacing-md);
    border: none;
    background: transparent;
    color: var(--text-secondary);
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: var(--transition);
    font-weight: 500;
    font-size: 0.875rem;
}

.filter-btn:hover {
    background: var(--bg-tertiary);
    color: var(--text-primary);
}

.filter-btn.active {
    background: var(--accent-primary);
    color: white;
}

.clear-btn {
    padding: var(--spacing-sm) var(--spacing-md);
    background: transparent;
    color: var(--danger);
    border: 1px solid var(--danger);
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: var(--transition);
    font-weight: 500;
    font-size: 0.875rem;
}

.clear-btn:hover {
    background: var(--danger);
    color: white;
}

/* Tasks Section */
.tasks-section {
    position: relative;
}

.tasks-list {
    list-style: none;
    display: flex;
    flex-direction: column;
    gap: var(--spacing-sm);
}

.task-item {
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
    padding: var(--spacing-lg);
    background: var(--bg-secondary);
    border-radius: var(--radius-lg);
    border: 1px solid var(--border);
    transition: var(--transition-slow);
    animation: slideIn 0.3s ease-out;
}

.task-item:hover {
    transform: translateY(-1px);
    box-shadow: 0 4px 12px var(--shadow);
}

.task-item.completed {
    opacity: 0.7;
}

.task-item.completed .task-text {
    text-decoration: line-through;
    color: var(--text-muted);
}

.task-checkbox {
    width: 20px;
    height: 20px;
    border: 2px solid var(--border);
    border-radius: var(--radius-sm);
    cursor: pointer;
    position: relative;
    transition: var(--transition);
    flex-shrink: 0;
}

.task-checkbox:hover {
    border-color: var(--accent-primary);
}

.task-checkbox.checked {
    background: var(--success);
    border-color: var(--success);
}

.task-checkbox.checked::after {
    content: '✓';
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    color: white;
    font-size: 0.75rem;
    font-weight: 700;
    animation: checkmark 0.3s ease-out;
}

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

.task-actions {
    display: flex;
    gap: var(--spacing-sm);
    opacity: 0;
    transition: var(--transition);
}

.task-item:hover .task-actions {
    opacity: 1;
}

.delete-btn {
    width: 32px;
    height: 32px;
    border: none;
    background: var(--danger);
    color: white;
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: var(--transition);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 0.875rem;
}

.delete-btn:hover {
    background: #dc2626;
    transform: scale(1.1);
}

/* Empty State */
.empty-state {
    text-align: center;
    padding: var(--spacing-2xl);
    color: var(--text-muted);
}

.empty-state.hidden {
    display: none;
}

.empty-icon {
    font-size: 3rem;
    margin-bottom: var(--spacing-md);
    opacity: 0.5;
}

.empty-state h3 {
    font-size: 1.25rem;
    margin-bottom: var(--spacing-sm);
    color: var(--text-secondary);
}

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

/* Animations */
@keyframes slideIn {
    from {
        opacity: 0;
        transform: translateY(-10px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

@keyframes slideOut {
    from {
        opacity: 1;
        transform: translateX(0);
    }
    to {
        opacity: 0;
        transform: translateX(100%);
    }
}

@keyframes checkmark {
    from {
        opacity: 0;
        transform: translate(-50%, -50%) scale(0);
    }
    to {
        opacity: 1;
        transform: translate(-50%, -50%) scale(1);
    }
}

.task-item.removing {
    animation: slideOut 0.3s ease-out forwards;
}

/* Responsive Design */
@media (max-width: 640px) {
    .container {
        padding: var(--spacing-sm);
    }
    
    .header {
        margin-bottom: var(--spacing-lg);
    }
    
    .logo h1 {
        font-size: 1.5rem;
    }
    
    .logo-icon {
        width: 40px;
        height: 40px;
        font-size: 1.25rem;
    }
    
    .theme-toggle {
        width: 40px;
        height: 40px;
        font-size: 1rem;
    }
    
    .app {
        padding: var(--spacing-lg);
    }
    
    .input-container {
        flex-direction: column;
    }
    
    #taskInput {
        min-width: unset;
    }
    
    .stats {
        padding: var(--spacing-md);
    }
    
    .stat-number {
        font-size: 1.25rem;
    }
    
    .filter-section {
        flex-direction: column;
        align-items: stretch;
    }
    
    .filters {
        justify-content: center;
    }
    
    .task-item {
        padding: var(--spacing-md);
    }
    
    .task-actions {
        opacity: 1;
    }
}

@media (max-width: 480px) {
    .stats {
        flex-direction: column;
        gap: var(--spacing-md);
    }
    
    .stat-item {
        flex-direction: row;
        justify-content: space-between;
    }
}