/* CSS Variables for Themes */
:root {
    --bg-color: #ffffff;
    --text-color: #333333;
    --accent-color: #4a90e2;
    --secondary-bg: #f5f5f5;
    --card-bg: #ffffff;
    --border-color: #e0e0e0;
    --shadow: rgba(0, 0, 0, 0.1);
    --gradient: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    --hover-bg: #f0f0f0;
    --completed-color: #28a745;
    --delete-color: #dc3545;
}

[data-theme="dark"] {
    --bg-color: #1a1a1a;
    --text-color: #ffffff;
    --accent-color: #7c3aed;
    --secondary-bg: #2d2d2d;
    --card-bg: #2d2d2d;
    --border-color: #404040;
    --shadow: rgba(0, 0, 0, 0.3);
    --gradient: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    --hover-bg: #404040;
    --completed-color: #28a745;
    --delete-color: #dc3545;
}

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

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background: var(--bg-color);
    color: var(--text-color);
    transition: background 0.3s ease, color 0.3s ease;
    min-height: 100vh;
    padding: 20px;
}

.container {
    max-width: 800px;
    margin: 0 auto;
    background: var(--card-bg);
    border-radius: 20px;
    box-shadow: 0 10px 30px var(--shadow);
    overflow: hidden;
    padding: 30px;
}

/* Header */
header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 30px;
    padding-bottom: 20px;
    border-bottom: 1px solid var(--border-color);
}

h1 {
    font-size: 2.5rem;
    font-weight: 700;
    background: var(--gradient);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

#theme-toggle {
    background: none;
    border: none;
    font-size: 1.5rem;
    cursor: pointer;
    padding: 10px;
    border-radius: 50%;
    transition: background 0.3s ease;
}

#theme-toggle:hover {
    background: var(--hover-bg);
}

/* Input Section */
.input-section {
    display: flex;
    gap: 15px;
    margin-bottom: 30px;
}

#task-input {
    flex: 1;
    padding: 15px 20px;
    border: 2px solid var(--border-color);
    border-radius: 50px;
    font-size: 1rem;
    background: var(--card-bg);
    color: var(--text-color);
    transition: border-color 0.3s ease, box-shadow 0.3s ease;
}

#task-input:focus {
    outline: none;
    border-color: var(--accent-color);
    box-shadow: 0 0 0 3px rgba(74, 144, 226, 0.1);
}

#add-task-btn {
    padding: 15px 30px;
    background: var(--gradient);
    color: white;
    border: none;
    border-radius: 50px;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: transform 0.2s ease, box-shadow 0.2s ease;
}

#add-task-btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 5px 15px rgba(0, 0, 0, 0.2);
}

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

/* Progress Section */
.progress-section {
    margin-bottom: 30px;
}

.progress-bar {
    width: 100%;
    height: 10px;
    background: var(--secondary-bg);
    border-radius: 5px;
    overflow: hidden;
    margin-bottom: 10px;
}

.progress-fill {
    height: 100%;
    background: var(--gradient);
    width: 0%;
    transition: width 0.5s ease;
}

.progress-text {
    text-align: center;
    font-size: 0.9rem;
    color: var(--text-color);
    opacity: 0.8;
}

/* Filters */
.filters {
    display: flex;
    gap: 10px;
    margin-bottom: 30px;
    flex-wrap: wrap;
}

.filter-btn, #clear-completed {
    padding: 10px 20px;
    background: var(--secondary-bg);
    color: var(--text-color);
    border: 1px solid var(--border-color);
    border-radius: 25px;
    cursor: pointer;
    font-size: 0.9rem;
    transition: all 0.3s ease;
}

.filter-btn:hover, #clear-completed:hover {
    background: var(--hover-bg);
}

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

/* Task List */
.task-list {
    margin-bottom: 30px;
}

.task-item {
    display: flex;
    align-items: center;
    padding: 20px;
    background: var(--card-bg);
    border: 1px solid var(--border-color);
    border-radius: 15px;
    margin-bottom: 15px;
    transition: all 0.3s ease;
    box-shadow: 0 2px 10px var(--shadow);
}

.task-item:hover {
    transform: translateY(-2px);
    box-shadow: 0 5px 20px var(--shadow);
}

.task-item.completed .task-text {
    text-decoration: line-through;
    opacity: 0.6;
}

.task-checkbox {
    margin-right: 15px;
    width: 20px;
    height: 20px;
    cursor: pointer;
}

.task-text {
    flex: 1;
    font-size: 1rem;
    word-break: break-word;
}

.task-text.editing {
    display: none;
}

.task-edit-input {
    flex: 1;
    padding: 10px;
    border: 1px solid var(--border-color);
    border-radius: 5px;
    font-size: 1rem;
    background: var(--card-bg);
    color: var(--text-color);
    display: none;
}

.task-edit-input.editing {
    display: block;
}

.task-actions {
    display: flex;
    gap: 10px;
}

.task-edit-btn, .task-delete-btn {
    padding: 8px 12px;
    border: none;
    border-radius: 20px;
    cursor: pointer;
    font-size: 0.8rem;
    transition: all 0.2s ease;
}

.task-edit-btn {
    background: var(--accent-color);
    color: white;
}

.task-edit-btn:hover {
    background: #357abd;
}

.task-delete-btn {
    background: var(--delete-color);
    color: white;
}

.task-delete-btn:hover {
    background: #c82333;
}

/* Empty State */
.empty-state {
    text-align: center;
    padding: 50px 20px;
    color: var(--text-color);
    opacity: 0.6;
    font-size: 1.1rem;
}

/* Responsive Design */
@media (max-width: 768px) {
    .container {
        padding: 20px;
        margin: 10px;
    }
    
    h1 {
        font-size: 2rem;
    }
    
    .input-section {
        flex-direction: column;
        gap: 10px;
    }
    
    #add-task-btn {
        align-self: stretch;
    }
    
    .filters {
        justify-content: center;
    }
    
    .task-item {
        padding: 15px;
        flex-direction: column;
        align-items: flex-start;
        gap: 10px;
    }
    
    .task-actions {
        align-self: flex-end;
    }
}

@media (max-width: 480px) {
    body {
        padding: 10px;
    }
    
    .container {
        padding: 15px;
    }
    
    h1 {
        font-size: 1.8rem;
    }
    
    .progress-text {
        font-size: 0.8rem;
    }
    
    .filter-btn, #clear-completed {
        padding: 8px 15px;
        font-size: 0.8rem;
    }
    
    .task-item {
        padding: 12px;
    }
    
    .task-text, .task-edit-input {
        font-size: 0.9rem;
    }
}

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

.task-item {
    animation: fadeIn 0.3s ease;
}

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

@keyframes fadeOut {
    from {
        opacity: 1;
        transform: translateY(0) scale(1);
    }
    to {
        opacity: 0;
        transform: translateY(-20px) scale(0.95);
    }
}

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