:root {
    --primary-color: #4a90e2;
    --secondary-color: #f5f5f5;
    --text-color: #333;
    --danger-color: #e74c3c;
    --success-color: #2ecc71;
    --border-radius: 8px;
    --transition: all 0.3s ease;
    --bg-color: #f9f9f9;
    --card-bg-color: white;
    --border-color: #eee;
    --input-border-color: #e1e1e1;
}

[data-theme="dark"] {
    --primary-color: #5c9ee6;
    --secondary-color: #2c2c2c;
    --text-color: #e0e0e0;
    --danger-color: #ff5f5f;
    --success-color: #3ee490;
    --bg-color: #1a1a1a;
    --card-bg-color: #2c2c2c;
    --border-color: #404040;
    --input-border-color: #404040;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
    line-height: 1.6;
    color: var(--text-color);
    background-color: var(--bg-color);
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    transition: var(--transition);
}

header {
    background-color: var(--primary-color);
    color: white;
    padding: 2rem;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}

.header-content {
    max-width: 800px;
    margin: 0 auto;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.theme-toggle {
    background: transparent;
    border: 2px solid white;
    color: white;
    padding: 0.5rem 1rem;
    border-radius: var(--border-radius);
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: 0.5rem;
    transition: var(--transition);
}

.theme-toggle:hover {
    background-color: rgba(255, 255, 255, 0.1);
}

.theme-toggle-icon {
    font-size: 1.2rem;
}

main {
    max-width: 800px;
    margin: 0 auto;
    padding: 2rem;
    flex: 1;
}

.task-input {
    background-color: var(--card-bg-color);
    padding: 2rem;
    border-radius: var(--border-radius);
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.05);
    margin-bottom: 2rem;
    transition: var(--transition);
}

.input-group {
    margin-bottom: 1rem;
}

label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 500;
}

input[type="text"] {
    width: 100%;
    padding: 0.75rem;
    border: 2px solid var(--input-border-color);
    border-radius: var(--border-radius);
    font-size: 1rem;
    transition: var(--transition);
    background-color: var(--card-bg-color);
    color: var(--text-color);
}

input[type="text"]:focus {
    outline: none;
    border-color: var(--primary-color);
}

.btn-add {
    background-color: var(--primary-color);
    color: white;
    border: none;
    padding: 0.75rem 1.5rem;
    border-radius: var(--border-radius);
    cursor: pointer;
    font-size: 1rem;
    transition: var(--transition);
}

.btn-add:hover {
    background-color: #357abd;
    transform: translateY(-1px);
}

.task-list {
    background-color: var(--card-bg-color);
    padding: 2rem;
    border-radius: var(--border-radius);
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.05);
    transition: var(--transition);
}

.task-filters {
    display: flex;
    gap: 1rem;
    margin-bottom: 2rem;
    flex-wrap: wrap;
}

.filter-btn {
    background-color: var(--secondary-color);
    border: none;
    padding: 0.75rem 1.5rem;
    border-radius: var(--border-radius);
    cursor: pointer;
    font-size: 1rem;
    transition: var(--transition);
    color: var(--text-color);
}

.filter-btn:hover {
    background-color: #e8e8e8;
}

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

#tasks {
    list-style: none;
}

.task-item {
    display: flex;
    align-items: center;
    padding: 1rem;
    border-bottom: 1px solid #eee;
    animation: slideIn 0.3s ease;
}

.task-item:last-child {
    border-bottom: none;
}

.task-text {
    flex: 1;
    margin: 0 1rem;
}

.task-completed {
    text-decoration: line-through;
    color: #888;
}

.task-actions {
    display: flex;
    gap: 0.5rem;
}

.btn-complete, .btn-delete {
    border: none;
    padding: 0.5rem;
    border-radius: var(--border-radius);
    cursor: pointer;
    transition: var(--transition);
}

.btn-complete {
    background-color: var(--success-color);
    color: white;
}

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

.btn-complete:hover, .btn-delete:hover {
    opacity: 0.9;
    transform: scale(1.05);
}

footer {
    text-align: center;
    padding: 1.5rem;
    background-color: var(--secondary-color);
    margin-top: auto;
}

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

/* Responsive Design */
@media (max-width: 600px) {
    main {
        padding: 1rem;
    }

    .task-input, .task-list {
        padding: 1rem;
    }

    .task-item {
        flex-direction: column;
        align-items: flex-start;
    }

    .task-actions {
        margin-top: 0.5rem;
        width: 100%;
        justify-content: flex-end;
    }
}