/* ========================================
   Simple To-Do List - Style Sheet
   Modern, minimal and user-friendly design
   ======================================== */

/* CSS Variables - Theme Colors */
:root {
    /* Base Colors - Dark theme */
    --color-bg-primary: #0f0f12;
    --color-bg-secondary: #1a1a21;
    --color-bg-tertiary: #24242e;
    --color-bg-hover: #2d2d3a;
    
    /* Accent Colors */
    --color-accent: #00d4aa;
    --color-accent-hover: #00eabb;
    --color-accent-dim: rgba(0, 212, 170, 0.15);
    
    /* Text Colors */
    --color-text-primary: #f5f5f7;
    --color-text-secondary: #9999a8;
    --color-text-muted: #6b6b7a;
    
    /* Status Colors */
    --color-success: #00d4aa;
    --color-danger: #ff5b6a;
    --color-danger-hover: #ff7a86;
    --color-warning: #ffb84d;
    
    /* Border and Shadow */
    --color-border: #2a2a36;
    --color-border-focus: var(--color-accent);
    --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);
    --shadow-glow: 0 0 20px rgba(0, 212, 170, 0.2);
    
    /* Sizes */
    --border-radius-sm: 6px;
    --border-radius-md: 10px;
    --border-radius-lg: 16px;
    --border-radius-full: 50px;
    
    /* Transition Durations */
    --transition-fast: 150ms ease;
    --transition-normal: 250ms ease;
    --transition-slow: 400ms ease;
    
    /* Font */
    --font-primary: 'Outfit', -apple-system, BlinkMacSystemFont, sans-serif;
    --font-mono: 'JetBrains Mono', 'Fira Code', monospace;
}

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

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

body {
    font-family: var(--font-primary);
    font-weight: 400;
    line-height: 1.6;
    color: var(--color-text-primary);
    background-color: var(--color-bg-primary);
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: flex-start;
    padding: 40px 20px;
    
    /* Background pattern */
    background-image: 
        radial-gradient(ellipse at top, rgba(0, 212, 170, 0.08) 0%, transparent 50%),
        radial-gradient(circle at 80% 20%, rgba(0, 212, 170, 0.05) 0%, transparent 30%),
        linear-gradient(180deg, var(--color-bg-primary) 0%, #0a0a0d 100%);
    background-attachment: fixed;
}

/* Focus Visible for Accessibility */
:focus-visible {
    outline: 2px solid var(--color-accent);
    outline-offset: 2px;
}

/* Selection */
::selection {
    background-color: var(--color-accent-dim);
    color: var(--color-text-primary);
}

/* ========================================
   App Container
   ======================================== */
.app-container {
    width: 100%;
    max-width: 560px;
    animation: fadeInUp 0.6s ease forwards;
}

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

/* ========================================
   Header Section
   ======================================== */
.app-header {
    text-align: center;
    margin-bottom: 40px;
    animation: fadeInUp 0.6s ease forwards;
    animation-delay: 0.1s;
    opacity: 0;
}

.app-title {
    font-size: 2.5rem;
    font-weight: 700;
    letter-spacing: -0.02em;
    margin-bottom: 8px;
    background: linear-gradient(135deg, var(--color-text-primary) 0%, var(--color-accent) 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.app-subtitle {
    font-size: 1rem;
    color: var(--color-text-secondary);
    font-weight: 300;
}

/* ========================================
   Add Todo Section
   ======================================== */
.add-todo-section {
    margin-bottom: 24px;
    animation: fadeInUp 0.6s ease forwards;
    animation-delay: 0.2s;
    opacity: 0;
}

.todo-form {
    display: flex;
    gap: 12px;
    background: var(--color-bg-secondary);
    padding: 8px;
    border-radius: var(--border-radius-lg);
    border: 1px solid var(--color-border);
    box-shadow: var(--shadow-md);
    transition: border-color var(--transition-normal), box-shadow var(--transition-normal);
}

.todo-form:focus-within {
    border-color: var(--color-accent);
    box-shadow: var(--shadow-md), var(--shadow-glow);
}

.todo-input {
    flex: 1;
    background: transparent;
    border: none;
    padding: 14px 16px;
    font-size: 1rem;
    font-family: var(--font-primary);
    color: var(--color-text-primary);
    outline: none;
}

.todo-input::placeholder {
    color: var(--color-text-muted);
}

/* ========================================
   Buttons
   ======================================== */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    padding: 12px 20px;
    font-family: var(--font-primary);
    font-size: 0.9rem;
    font-weight: 500;
    border: none;
    border-radius: var(--border-radius-md);
    cursor: pointer;
    transition: all var(--transition-fast);
    white-space: nowrap;
}

.btn .icon {
    width: 18px;
    height: 18px;
    flex-shrink: 0;
}

.btn-add {
    background: var(--color-accent);
    color: var(--color-bg-primary);
}

.btn-add:hover {
    background: var(--color-accent-hover);
    transform: scale(1.02);
}

.btn-add:active {
    transform: scale(0.98);
}

.btn-clear {
    background: transparent;
    color: var(--color-text-secondary);
    border: 1px solid var(--color-border);
    padding: 10px 16px;
    font-size: 0.85rem;
}

.btn-clear:hover {
    color: var(--color-danger);
    border-color: var(--color-danger);
    background: rgba(255, 91, 106, 0.1);
}

/* ========================================
   Filters Section
   ======================================== */
.filters-section {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 20px;
    padding: 0 4px;
    animation: fadeInUp 0.6s ease forwards;
    animation-delay: 0.3s;
    opacity: 0;
}

.filter-buttons {
    display: flex;
    gap: 4px;
    background: var(--color-bg-secondary);
    padding: 4px;
    border-radius: var(--border-radius-full);
    border: 1px solid var(--color-border);
}

.filter-btn {
    padding: 8px 16px;
    font-family: var(--font-primary);
    font-size: 0.85rem;
    font-weight: 500;
    color: var(--color-text-secondary);
    background: transparent;
    border: none;
    border-radius: var(--border-radius-full);
    cursor: pointer;
    transition: all var(--transition-fast);
}

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

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

.todo-stats {
    display: flex;
    align-items: center;
}

.todo-count {
    font-size: 0.85rem;
    font-family: var(--font-mono);
    color: var(--color-text-muted);
}

/* ========================================
   Todo List Section
   ======================================== */
.todo-list-section {
    animation: fadeInUp 0.6s ease forwards;
    animation-delay: 0.4s;
    opacity: 0;
}

.todo-list {
    list-style: none;
    display: flex;
    flex-direction: column;
    gap: 10px;
}

/* ========================================
   Todo Item
   ======================================== */
.todo-item {
    display: flex;
    align-items: center;
    gap: 14px;
    padding: 16px 18px;
    background: var(--color-bg-secondary);
    border-radius: var(--border-radius-md);
    border: 1px solid var(--color-border);
    transition: all var(--transition-normal);
    animation: slideIn 0.3s ease forwards;
    cursor: grab;
}

.todo-item:hover {
    background: var(--color-bg-tertiary);
    border-color: var(--color-border-focus);
    transform: translateX(4px);
}

.todo-item.dragging {
    opacity: 0.5;
    cursor: grabbing;
    transform: scale(1.02);
    box-shadow: var(--shadow-lg);
}

.todo-item.drag-over-top {
    box-shadow: inset 0 3px 0 var(--color-accent);
}

.todo-item.drag-over-bottom {
    box-shadow: inset 0 -3px 0 var(--color-accent);
}

.todo-item.completed {
    opacity: 0.6;
}

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

@keyframes slideIn {
    from {
        opacity: 0;
        transform: translateX(-20px);
    }
    to {
        opacity: 1;
        transform: translateX(0);
    }
}

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

/* Checkbox */
.todo-checkbox {
    position: relative;
    width: 24px;
    height: 24px;
    flex-shrink: 0;
}

.todo-checkbox input {
    position: absolute;
    opacity: 0;
    width: 100%;
    height: 100%;
    cursor: pointer;
    z-index: 1;
}

.todo-checkbox .checkmark {
    position: absolute;
    top: 0;
    left: 0;
    width: 24px;
    height: 24px;
    background: transparent;
    border: 2px solid var(--color-text-muted);
    border-radius: 50%;
    transition: all var(--transition-fast);
    display: flex;
    align-items: center;
    justify-content: center;
}

.todo-checkbox .checkmark svg {
    width: 14px;
    height: 14px;
    stroke: var(--color-bg-primary);
    opacity: 0;
    transform: scale(0);
    transition: all var(--transition-fast);
}

.todo-checkbox input:hover + .checkmark {
    border-color: var(--color-accent);
}

.todo-checkbox input:checked + .checkmark {
    background: var(--color-accent);
    border-color: var(--color-accent);
}

.todo-checkbox input:checked + .checkmark svg {
    opacity: 1;
    transform: scale(1);
}

/* Todo Text */
.todo-text {
    flex: 1;
    font-size: 1rem;
    color: var(--color-text-primary);
    word-break: break-word;
    transition: all var(--transition-fast);
}

/* Edit Input */
.todo-edit-input {
    flex: 1;
    background: var(--color-bg-primary);
    border: 1px solid var(--color-accent);
    border-radius: var(--border-radius-sm);
    padding: 8px 12px;
    font-family: var(--font-primary);
    font-size: 1rem;
    color: var(--color-text-primary);
    outline: none;
}

/* Todo Actions */
.todo-actions {
    display: flex;
    gap: 6px;
    opacity: 0;
    transition: opacity var(--transition-fast);
}

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

.todo-action-btn {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 34px;
    height: 34px;
    background: var(--color-bg-primary);
    border: 1px solid var(--color-border);
    border-radius: var(--border-radius-sm);
    color: var(--color-text-secondary);
    cursor: pointer;
    transition: all var(--transition-fast);
}

.todo-action-btn svg {
    width: 16px;
    height: 16px;
}

.todo-action-btn:hover {
    color: var(--color-text-primary);
    border-color: var(--color-text-muted);
}

.todo-action-btn.edit:hover {
    color: var(--color-warning);
    border-color: var(--color-warning);
    background: rgba(255, 184, 77, 0.1);
}

.todo-action-btn.delete:hover {
    color: var(--color-danger);
    border-color: var(--color-danger);
    background: rgba(255, 91, 106, 0.1);
}

.todo-action-btn.save {
    color: var(--color-success);
    border-color: var(--color-success);
}

.todo-action-btn.save:hover {
    background: rgba(0, 212, 170, 0.1);
}

.todo-action-btn.cancel:hover {
    color: var(--color-danger);
    border-color: var(--color-danger);
    background: rgba(255, 91, 106, 0.1);
}

/* Drag Handle */
.drag-handle {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 20px;
    color: var(--color-text-muted);
    opacity: 0;
    transition: opacity var(--transition-fast);
    cursor: grab;
}

.drag-handle svg {
    width: 16px;
    height: 16px;
}

.todo-item:hover .drag-handle {
    opacity: 0.6;
}

.todo-item:hover .drag-handle:hover {
    opacity: 1;
}

/* ========================================
   Empty State
   ======================================== */
.empty-state {
    display: none;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    padding: 60px 20px;
    text-align: center;
    animation: fadeIn 0.4s ease;
}

.empty-state.show {
    display: flex;
}

@keyframes fadeIn {
    from { opacity: 0; }
    to { opacity: 1; }
}

.empty-icon {
    width: 80px;
    height: 80px;
    margin-bottom: 20px;
    color: var(--color-text-muted);
    opacity: 0.5;
}

.empty-icon svg {
    width: 100%;
    height: 100%;
}

.empty-text {
    font-size: 1.1rem;
    font-weight: 500;
    color: var(--color-text-secondary);
    margin-bottom: 8px;
}

.empty-hint {
    font-size: 0.9rem;
    color: var(--color-text-muted);
}

/* ========================================
   Footer Section
   ======================================== */
.app-footer {
    display: flex;
    justify-content: center;
    margin-top: 24px;
    padding-top: 24px;
    border-top: 1px solid var(--color-border);
    animation: fadeInUp 0.6s ease forwards;
    animation-delay: 0.5s;
    opacity: 0;
}

.app-footer .btn-clear {
    opacity: 0;
    pointer-events: none;
    transition: opacity var(--transition-normal);
}

.app-footer .btn-clear.show {
    opacity: 1;
    pointer-events: auto;
}

/* ========================================
   Responsive Design
   ======================================== */
@media (max-width: 480px) {
    body {
        padding: 24px 16px;
    }
    
    .app-title {
        font-size: 2rem;
    }
    
    .todo-form {
        flex-direction: column;
    }
    
    .btn-add {
        width: 100%;
    }
    
    .filters-section {
        flex-direction: column;
        gap: 12px;
    }
    
    .filter-buttons {
        width: 100%;
        justify-content: center;
    }
    
    .todo-actions {
        opacity: 1;
    }
    
    .drag-handle {
        opacity: 0.4;
    }
}

/* ========================================
   Utility Classes
   ======================================== */
.hidden {
    display: none !important;
}

.visually-hidden {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    border: 0;
}