/* ===== CSS CUSTOM PROPERTIES ===== */
:root {
    /* Light Theme Colors */
    --color-primary: #3b82f6;
    --color-primary-dark: #2563eb;
    --color-secondary: #64748b;
    --color-success: #10b981;
    --color-warning: #f59e0b;
    --color-danger: #ef4444;
    
    /* Background Colors */
    --color-bg-primary: #ffffff;
    --color-bg-secondary: #f8fafc;
    --color-bg-tertiary: #f1f5f9;
    --color-surface: #ffffff;
    --color-surface-hover: #f8fafc;
    
    /* Text Colors */
    --color-text-primary: #0f172a;
    --color-text-secondary: #475569;
    --color-text-tertiary: #64748b;
    --color-text-inverse: #ffffff;
    
    /* Border Colors */
    --color-border-light: #e2e8f0;
    --color-border-medium: #cbd5e1;
    --color-border-dark: #94a3b8;
    
    /* Shadow Colors */
    --shadow-light: 0 1px 3px 0 rgb(0 0 0 / 0.1), 0 1px 2px -1px rgb(0 0 0 / 0.1);
    --shadow-medium: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
    --shadow-large: 0 10px 15px -3px rgb(0 0 0 / 0.1), 0 4px 6px -4px rgb(0 0 0 / 0.1);
    
    /* Typography */
    --font-family-primary: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    --font-size-xs: 0.75rem;
    --font-size-sm: 0.875rem;
    --font-size-base: 1rem;
    --font-size-lg: 1.125rem;
    --font-size-xl: 1.25rem;
    --font-size-2xl: 1.5rem;
    --font-size-3xl: 1.875rem;
    
    /* 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-fast: 0.15s ease-in-out;
    --transition-medium: 0.3s ease-in-out;
    --transition-slow: 0.5s ease-in-out;
    
    /* Z-Index Scale */
    --z-dropdown: 1000;
    --z-modal: 2000;
    --z-tooltip: 3000;
    --z-toast: 4000;
}

/* Dark Theme */
[data-theme="dark"] {
    --color-bg-primary: #0f172a;
    --color-bg-secondary: #1e293b;
    --color-bg-tertiary: #334155;
    --color-surface: #1e293b;
    --color-surface-hover: #334155;
    
    --color-text-primary: #f8fafc;
    --color-text-secondary: #cbd5e1;
    --color-text-tertiary: #94a3b8;
    
    --color-border-light: #334155;
    --color-border-medium: #475569;
    --color-border-dark: #64748b;
    
    --shadow-light: 0 1px 3px 0 rgb(0 0 0 / 0.3);
    --shadow-medium: 0 4px 6px -1px rgb(0 0 0 / 0.3);
    --shadow-large: 0 10px 15px -3px rgb(0 0 0 / 0.3);
}

/* ===== RESET & BASE STYLES ===== */
*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

html {
    font-size: 16px;
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-family-primary);
    font-size: var(--font-size-base);
    line-height: 1.5;
    color: var(--color-text-primary);
    background-color: var(--color-bg-primary);
    transition: background-color var(--transition-medium), color var(--transition-medium);
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

/* ===== LAYOUT COMPONENTS ===== */
.app-container {
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    max-width: 768px;
    margin: 0 auto;
    background-color: var(--color-surface);
    box-shadow: var(--shadow-large);
}

/* Header */
.app-header {
    background: linear-gradient(135deg, var(--color-primary), var(--color-primary-dark));
    color: var(--color-text-inverse);
    padding: var(--spacing-xl) var(--spacing-lg);
    position: sticky;
    top: 0;
    z-index: 100;
}

.header-content {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: var(--spacing-md);
}

.logo-section {
    flex: 1;
}

.app-title {
    font-size: var(--font-size-2xl);
    font-weight: 700;
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    margin-bottom: var(--spacing-xs);
}

.logo-icon {
    font-size: var(--font-size-3xl);
    animation: bounce 2s infinite;
}

.app-tagline {
    font-size: var(--font-size-sm);
    opacity: 0.9;
    font-weight: 400;
}

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

.theme-toggle {
    background: rgba(255, 255, 255, 0.2);
    border: 1px solid rgba(255, 255, 255, 0.3);
    color: white;
    padding: var(--spacing-sm);
    border-radius: var(--radius-md);
    cursor: pointer;
    font-size: var(--font-size-lg);
    transition: all var(--transition-fast);
    backdrop-filter: blur(10px);
}

.theme-toggle:hover {
    background: rgba(255, 255, 255, 0.3);
    transform: scale(1.05);
}

.task-counter {
    font-size: var(--font-size-sm);
    font-weight: 600;
    padding: var(--spacing-xs) var(--spacing-sm);
    background: rgba(255, 255, 255, 0.2);
    border-radius: var(--radius-lg);
    backdrop-filter: blur(10px);
}

/* Main Content */
.main-content {
    flex: 1;
    padding: var(--spacing-xl) var(--spacing-lg);
    display: flex;
    flex-direction: column;
    gap: var(--spacing-xl);
}

/* Task Input Section */
.task-input-section {
    background: var(--color-surface);
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    box-shadow: var(--shadow-medium);
    border: 1px solid var(--color-border-light);
}

.input-group {
    display: flex;
    gap: var(--spacing-sm);
    margin-bottom: var(--spacing-md);
}

.task-input {
    flex: 1;
    padding: var(--spacing-md);
    font-size: var(--font-size-base);
    border: 2px solid var(--color-border-light);
    border-radius: var(--radius-md);
    background: var(--color-bg-secondary);
    color: var(--color-text-primary);
    transition: all var(--transition-fast);
    font-family: inherit;
}

.task-input:focus {
    outline: none;
    border-color: var(--color-primary);
    box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.1);
    background: var(--color-surface);
}

.task-input::placeholder {
    color: var(--color-text-tertiary);
}

.add-btn {
    background: var(--color-primary);
    color: white;
    border: none;
    padding: var(--spacing-md);
    border-radius: var(--radius-md);
    cursor: pointer;
    font-size: var(--font-size-xl);
    font-weight: 600;
    min-width: 48px;
    transition: all var(--transition-fast);
    display: flex;
    align-items: center;
    justify-content: center;
}

.add-btn:hover {
    background: var(--color-primary-dark);
    transform: translateY(-1px);
}

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

.error-message {
    color: var(--color-danger);
    font-size: var(--font-size-sm);
    margin-top: var(--spacing-xs);
    opacity: 0;
    transform: translateY(-4px);
    transition: all var(--transition-fast);
}

.error-message.show {
    opacity: 1;
    transform: translateY(0);
}

.input-footer {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.character-count {
    color: var(--color-text-tertiary);
    font-size: var(--font-size-xs);
}

/* Filter Section */
.filter-section {
    display: flex;
    gap: var(--spacing-xs);
    background: var(--color-bg-secondary);
    padding: var(--spacing-xs);
    border-radius: var(--radius-lg);
    border: 1px solid var(--color-border-light);
}

.filter-btn {
    flex: 1;
    padding: var(--spacing-sm) var(--spacing-md);
    border: none;
    background: transparent;
    color: var(--color-text-secondary);
    border-radius: var(--radius-md);
    cursor: pointer;
    font-size: var(--font-size-sm);
    font-weight: 500;
    transition: all var(--transition-fast);
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-xs);
}

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

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

.filter-count {
    background: rgba(255, 255, 255, 0.2);
    padding: 2px var(--spacing-xs);
    border-radius: var(--radius-sm);
    font-size: var(--font-size-xs);
    font-weight: 600;
}

.filter-btn.active .filter-count {
    background: rgba(255, 255, 255, 0.3);
}

/* Task List */
.task-list-section {
    flex: 1;
    position: relative;
}

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

.task {
    background: var(--color-surface);
    border: 1px solid var(--color-border-light);
    border-radius: var(--radius-md);
    padding: var(--spacing-md);
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
    transition: all var(--transition-fast);
    cursor: pointer;
    position: relative;
}

.task:hover {
    border-color: var(--color-border-medium);
    box-shadow: var(--shadow-light);
    transform: translateY(-1px);
}

.task.completed {
    opacity: 0.7;
    background: var(--color-bg-tertiary);
}

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

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

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

.task-checkbox:checked::after {
    content: '✓';
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    color: white;
    font-size: var(--font-size-xs);
    font-weight: bold;
}

.task-content {
    flex: 1;
    min-width: 0;
}

.task-text {
    font-size: var(--font-size-base);
    color: var(--color-text-primary);
    word-wrap: break-word;
    line-height: 1.4;
}

.task-meta {
    display: flex;
    gap: var(--spacing-md);
    margin-top: var(--spacing-xs);
}

.task-date {
    font-size: var(--font-size-xs);
    color: var(--color-text-tertiary);
}

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

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

.task-btn {
    padding: var(--spacing-xs);
    border: none;
    background: transparent;
    cursor: pointer;
    border-radius: var(--radius-sm);
    font-size: var(--font-size-sm);
    transition: all var(--transition-fast);
    min-width: 32px;
    height: 32px;
    display: flex;
    align-items: center;
    justify-content: center;
}

.task-btn:hover {
    background: var(--color-surface-hover);
}

.edit-btn {
    color: var(--color-warning);
}

.delete-btn {
    color: var(--color-danger);
}

.delete-btn:hover {
    background: rgba(239, 68, 68, 0.1);
}

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

.empty-illustration svg {
    color: var(--color-text-tertiary);
    margin-bottom: var(--spacing-lg);
}

.empty-title {
    font-size: var(--font-size-xl);
    font-weight: 600;
    margin-bottom: var(--spacing-sm);
    color: var(--color-text-secondary);
}

.empty-description {
    font-size: var(--font-size-base);
}

/* Bulk Actions */
.bulk-actions {
    padding: var(--spacing-md);
    background: var(--color-bg-secondary);
    border-radius: var(--radius-md);
    border: 1px solid var(--color-border-light);
}

.bulk-controls {
    display: flex;
    gap: var(--spacing-sm);
    justify-content: center;
}

.bulk-btn {
    padding: var(--spacing-sm) var(--spacing-md);
    border: 1px solid var(--color-border-medium);
    background: var(--color-surface);
    color: var(--color-text-secondary);
    border-radius: var(--radius-md);
    cursor: pointer;
    font-size: var(--font-size-sm);
    font-weight: 500;
    transition: all var(--transition-fast);
    display: flex;
    align-items: center;
    gap: var(--spacing-xs);
}

.bulk-btn:hover {
    background: var(--color-surface-hover);
    border-color: var(--color-border-dark);
}

.bulk-btn.danger {
    color: var(--color-danger);
    border-color: var(--color-danger);
}

.bulk-btn.danger:hover {
    background: rgba(239, 68, 68, 0.1);
}

/* Footer */
.app-footer {
    background: var(--color-bg-secondary);
    border-top: 1px solid var(--color-border-light);
    padding: var(--spacing-lg);
    text-align: center;
}

.footer-text {
    font-size: var(--font-size-sm);
    color: var(--color-text-secondary);
    margin-bottom: var(--spacing-xs);
}

.footer-link {
    color: var(--color-primary);
    text-decoration: none;
}

.footer-link:hover {
    text-decoration: underline;
}

.footer-stats {
    font-size: var(--font-size-xs);
    color: var(--color-text-tertiary);
}

/* Modal */
.modal-overlay {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: rgba(0, 0, 0, 0.5);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: var(--z-modal);
    opacity: 0;
    visibility: hidden;
    transition: all var(--transition-medium);
    backdrop-filter: blur(4px);
}

.modal-overlay.show {
    opacity: 1;
    visibility: visible;
}

.modal-content {
    background: var(--color-surface);
    border-radius: var(--radius-lg);
    padding: var(--spacing-xl);
    max-width: 400px;
    width: 90%;
    box-shadow: var(--shadow-large);
    transform: scale(0.9);
    transition: transform var(--transition-medium);
}

.modal-overlay.show .modal-content {
    transform: scale(1);
}

.modal-title {
    font-size: var(--font-size-xl);
    font-weight: 600;
    margin-bottom: var(--spacing-md);
    color: var(--color-text-primary);
}

.modal-message {
    color: var(--color-text-secondary);
    margin-bottom: var(--spacing-xl);
    line-height: 1.5;
}

.modal-actions {
    display: flex;
    gap: var(--spacing-sm);
    justify-content: flex-end;
}

.modal-btn {
    padding: var(--spacing-sm) var(--spacing-md);
    border: none;
    border-radius: var(--radius-md);
    cursor: pointer;
    font-size: var(--font-size-sm);
    font-weight: 500;
    transition: all var(--transition-fast);
}

.modal-btn.primary {
    background: var(--color-primary);
    color: white;
}

.modal-btn.primary:hover {
    background: var(--color-primary-dark);
}

.modal-btn.secondary {
    background: var(--color-bg-secondary);
    color: var(--color-text-secondary);
    border: 1px solid var(--color-border-medium);
}

.modal-btn.secondary:hover {
    background: var(--color-surface-hover);
}

/* Loading Indicator */
.loading-indicator {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: rgba(255, 255, 255, 0.8);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: var(--z-modal);
}

[data-theme="dark"] .loading-indicator {
    background: rgba(0, 0, 0, 0.8);
}

.spinner {
    width: 40px;
    height: 40px;
    border: 4px solid var(--color-border-light);
    border-top: 4px solid var(--color-primary);
    border-radius: 50%;
    animation: spin 1s linear infinite;
}

/* Toast Notifications */
.toast-container {
    position: fixed;
    bottom: var(--spacing-xl);
    right: var(--spacing-xl);
    z-index: var(--z-toast);
    display: flex;
    flex-direction: column;
    gap: var(--spacing-sm);
}

.toast {
    background: var(--color-surface);
    border: 1px solid var(--color-border-light);
    border-radius: var(--radius-md);
    padding: var(--spacing-md);
    box-shadow: var(--shadow-large);
    min-width: 280px;
    transform: translateX(100%);
    transition: transform var(--transition-medium);
}

.toast.show {
    transform: translateX(0);
}

.toast.success {
    border-left: 4px solid var(--color-success);
}

.toast.error {
    border-left: 4px solid var(--color-danger);
}

.toast.warning {
    border-left: 4px solid var(--color-warning);
}

/* Animations */
@keyframes bounce {
    0%, 20%, 50%, 80%, 100% {
        transform: translateY(0);
    }
    40% {
        transform: translateY(-8px);
    }
    60% {
        transform: translateY(-4px);
    }
}

@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}

@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.task {
    animation: fadeInUp 0.3s ease-out;
}

/* Responsive Design */
@media (max-width: 640px) {
    .app-container {
        margin: 0;
        border-radius: 0;
        box-shadow: none;
    }
    
    .header-content {
        flex-direction: column;
        text-align: center;
        gap: var(--spacing-sm);
    }
    
    .main-content {
        padding: var(--spacing-lg) var(--spacing-md);
    }
    
    .task-input-section {
        padding: var(--spacing-md);
    }
    
    .input-group {
        flex-direction: column;
    }
    
    .filter-section {
        flex-direction: column;
        gap: var(--spacing-xs);
    }
    
    .filter-btn {
        justify-content: space-between;
        padding: var(--spacing-md);
    }
    
    .task {
        flex-direction: column;
        align-items: flex-start;
        gap: var(--spacing-sm);
    }
    
    .task-content {
        width: 100%;
    }
    
    .task-actions {
        opacity: 1;
        align-self: flex-end;
    }
    
    .bulk-controls {
        flex-direction: column;
    }
    
    .toast-container {
        bottom: var(--spacing-md);
        right: var(--spacing-md);
        left: var(--spacing-md);
    }
    
    .toast {
        min-width: auto;
    }
}

/* High contrast mode support */
@media (prefers-contrast: high) {
    :root {
        --color-border-light: #000000;
        --color-border-medium: #000000;
    }
    
    .task {
        border-width: 2px;
    }
}

/* Reduced motion support */
@media (prefers-reduced-motion: reduce) {
    *, *::before, *::after {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
    }
}

/* Print styles */
@media print {
    .app-header,
    .filter-section,
    .bulk-actions,
    .app-footer,
    .task-actions {
        display: none;
    }
    
    .main-content {
        padding: 0;
    }
    
    .task {
        border: 1px solid #000;
        break-inside: avoid;
        margin-bottom: 8px;
    }
}