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

:root {
    /* Color Palette - Light Theme */
    --color-bg: #f8f9fa;
    --color-surface: #ffffff;
    --color-primary: #4a6fa5;
    --color-primary-dark: #3a5a8a;
    --color-secondary: #6c757d;
    --color-success: #28a745;
    --color-danger: #dc3545;
    --color-text: #212529;
    --color-text-light: #6c757d;
    --color-border: #dee2e6;
    --color-shadow: rgba(0, 0, 0, 0.08);

    /* Typography */
    --font-family: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
    --font-size-xs: 0.75rem;   /* 12px */
    --font-size-sm: 0.875rem;  /* 14px */
    --font-size-base: 1rem;    /* 16px */
    --font-size-lg: 1.125rem;  /* 18px */
    --font-size-xl: 1.5rem;    /* 24px */
    --font-size-2xl: 2rem;     /* 32px */

    /* Spacing */
    --spacing-xs: 0.25rem;  /* 4px */
    --spacing-sm: 0.5rem;   /* 8px */
    --spacing-md: 1rem;     /* 16px */
    --spacing-lg: 1.5rem;   /* 24px */
    --spacing-xl: 2rem;     /* 32px */

    /* Border Radius */
    --radius-sm: 4px;
    --radius-md: 8px;
    --radius-lg: 12px;
    --radius-full: 9999px;

    /* Transitions */
    --transition-fast: 150ms ease;
    --transition-base: 250ms ease;
    --transition-slow: 350ms ease;
}

body {
    font-family: var(--font-family);
    font-size: var(--font-size-base);
    line-height: 1.5;
    color: var(--color-text);
    background-color: var(--color-bg);
    min-height: 100vh;
    padding: var(--spacing-md);
}

.container {
    max-width: 600px;
    margin: 0 auto;
    background-color: var(--color-surface);
    border-radius: var(--radius-lg);
    box-shadow: 0 4px 20px var(--color-shadow);
    overflow: hidden;
}

/* Header Styles */
.app-header {
    background: linear-gradient(135deg, var(--color-primary) 0%, var(--color-primary-dark) 100%);
    color: white;
    padding: var(--spacing-xl) var(--spacing-lg);
    text-align: center;
}

.app-header h1 {
    font-size: var(--font-size-2xl);
    font-weight: 700;
    margin-bottom: var(--spacing-xs);
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-sm);
}

.app-header .subtitle {
    font-size: var(--font-size-sm);
    opacity: 0.9;
    font-weight: 300;
}

/* Input Section */
.input-section {
    padding: var(--spacing-lg);
    border-bottom: 1px solid var(--color-border);
}

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

#taskInput {
    flex: 1;
    padding: var(--spacing-md) var(--spacing-lg);
    border: 2px solid var(--color-border);
    border-radius: var(--radius-md);
    font-size: var(--font-size-base);
    font-family: var(--font-family);
    transition: all var(--transition-base);
}

#taskInput:focus {
    outline: none;
    border-color: var(--color-primary);
    box-shadow: 0 0 0 3px rgba(74, 111, 165, 0.1);
}

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

.btn-primary {
    background-color: var(--color-primary);
    color: white;
    border: none;
    padding: var(--spacing-md) var(--spacing-lg);
    border-radius: var(--radius-md);
    font-size: var(--font-size-base);
    font-weight: 600;
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    transition: all var(--transition-base);
}

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

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

.btn-primary:disabled {
    background-color: var(--color-secondary);
    cursor: not-allowed;
    transform: none;
}

.input-hint {
    font-size: var(--font-size-xs);
    color: var(--color-text-light);
    text-align: center;
}

/* Filters Section */
.filters-section {
    padding: var(--spacing-md) var(--spacing-lg);
    border-bottom: 1px solid var(--color-border);
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: var(--spacing-md);
}

.filter-buttons {
    display: flex;
    gap: var(--spacing-sm);
}

.filter-btn {
    background: none;
    border: 1px solid var(--color-border);
    padding: var(--spacing-sm) var(--spacing-md);
    border-radius: var(--radius-sm);
    font-size: var(--font-size-sm);
    color: var(--color-text-light);
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: var(--spacing-xs);
    transition: all var(--transition-base);
}

.filter-btn:hover {
    border-color: var(--color-primary);
    color: var(--color-primary);
}

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

.task-counter {
    font-size: var(--font-size-sm);
    color: var(--color-text-light);
    font-weight: 500;
}

.task-counter span {
    font-weight: 700;
    color: var(--color-primary);
}

/* Tasks Section */
.tasks-section {
    min-height: 300px;
}

.task-list {
    list-style: none;
}

.task-list .empty-state {
    text-align: center;
    padding: var(--spacing-xl) var(--spacing-lg);
    color: var(--color-text-light);
}

.task-list .empty-state i {
    font-size: 3rem;
    margin-bottom: var(--spacing-md);
    color: var(--color-border);
}

.task-list .empty-state p {
    font-size: var(--font-size-base);
}

.task-item {
    display: flex;
    align-items: center;
    padding: var(--spacing-md) var(--spacing-lg);
    border-bottom: 1px solid var(--color-border);
    transition: all var(--transition-base);
    animation: fadeIn 300ms ease;
}

.task-item:hover {
    background-color: rgba(0, 0, 0, 0.02);
}

.task-checkbox {
    width: 24px;
    height: 24px;
    border: 2px solid var(--color-border);
    border-radius: var(--radius-sm);
    margin-right: var(--spacing-md);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    flex-shrink: 0;
    transition: all var(--transition-base);
}

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

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

.task-checkbox.completed i {
    font-size: var(--font-size-sm);
}

.task-text {
    flex: 1;
    font-size: var(--font-size-base);
    transition: all var(--transition-base);
    word-break: break-word;
    padding-right: var(--spacing-md);
}

.task-text.completed {
    text-decoration: line-through;
    color: var(--color-text-light);
    opacity: 0.7;
}

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

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

.btn-icon {
    background: none;
    border: none;
    width: 32px;
    height: 32px;
    border-radius: var(--radius-sm);
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    color: var(--color-text-light);
    transition: all var(--transition-base);
}

.btn-icon:hover {
    background-color: rgba(0, 0, 0, 0.05);
}

.btn-delete:hover {
    color: var(--color-danger);
    background-color: rgba(220, 53, 69, 0.1);
}

.btn-edit:hover {
    color: var(--color-primary);
    background-color: rgba(74, 111, 165, 0.1);
}

/* Footer */
.app-footer {
    padding: var(--spacing-md) var(--spacing-lg);
    text-align: center;
    font-size: var(--font-size-xs);
    color: var(--color-text-light);
    border-top: 1px solid var(--color-border);
    background-color: rgba(0, 0, 0, 0.02);
}

.app-footer p {
    margin-bottom: var(--spacing-xs);
}

.footer-note i {
    color: var(--color-danger);
}

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

@keyframes strikeThrough {
    from {
        text-decoration-color: transparent;
    }
    to {
        text-decoration-color: currentColor;
    }
}

.task-text.completed {
    animation: strikeThrough 300ms ease;
}

/* Responsive Design */
@media (max-width: 640px) {
    body {
        padding: var(--spacing-sm);
    }

    .container {
        border-radius: var(--radius-md);
    }

    .app-header {
        padding: var(--spacing-lg) var(--spacing-md);
    }

    .app-header h1 {
        font-size: var(--font-size-xl);
    }

    .input-group {
        flex-direction: column;
    }

    .btn-primary {
        justify-content: center;
    }

    .filters-section {
        flex-direction: column;
        align-items: stretch;
        gap: var(--spacing-sm);
    }

    .filter-buttons {
        justify-content: center;
    }

    .task-counter {
        text-align: center;
    }

    .task-item {
        padding: var(--spacing-md);
    }

    .task-actions {
        opacity: 1; /* Always show on mobile */
    }
}

@media (max-width: 480px) {
    .filter-buttons {
        flex-direction: column;
    }

    .filter-btn {
        justify-content: center;
    }
}

/* Utility Classes */
.visually-hidden {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border: 0;
}