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

:root {
    --primary-color: #3498db;
    --primary-dark: #2980b9;
    --success-color: #27ae60;
    --danger-color: #e74c3c;
    --warning-color: #f39c12;
    --bg-color: #f5f6fa;
    --card-bg: #ffffff;
    --text-primary: #2c3e50;
    --text-secondary: #7f8c8d;
    --border-color: #e0e0e0;
    --shadow: 0 2px 10px rgba(0, 0, 0, 0.1);
    --shadow-hover: 0 4px 20px rgba(0, 0, 0, 0.15);
    --radius: 12px;
    --transition: all 0.3s ease;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, sans-serif;
    background: var(--bg-color);
    color: var(--text-primary);
    min-height: 100vh;
    line-height: 1.6;
}

.app-container {
    max-width: 600px;
    margin: 0 auto;
    padding: 20px;
    min-height: 100vh;
}

.app-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 20px 0;
    margin-bottom: 20px;
}

.app-header h1 {
    font-size: 1.8rem;
    font-weight: 700;
    color: var(--text-primary);
}

.sync-status {
    display: flex;
    align-items: center;
    gap: 8px;
    padding: 8px 16px;
    background: var(--card-bg);
    border-radius: 20px;
    box-shadow: var(--shadow);
}

.status-indicator {
    width: 10px;
    height: 10px;
    border-radius: 50%;
    transition: var(--transition);
}

.status-indicator.online {
    background: var(--success-color);
    box-shadow: 0 0 10px var(--success-color);
}

.status-indicator.offline {
    background: var(--danger-color);
}

.status-indicator.syncing {
    background: var(--warning-color);
    animation: pulse 1s infinite;
}

@keyframes pulse {
    0%, 100% { opacity: 1; }
    50% { opacity: 0.5; }
}

.status-text {
    font-size: 0.85rem;
    color: var(--text-secondary);
}

.settings-panel {
    background: var(--card-bg);
    padding: 20px;
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    margin-bottom: 20px;
    display: none;
}

.settings-panel.visible {
    display: block;
    animation: slideDown 0.3s ease;
}

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

.setting-group {
    margin-bottom: 12px;
}

.setting-label {
    display: flex;
    align-items: center;
    gap: 10px;
    cursor: pointer;
    padding: 8px 0;
}

.setting-label input[type="checkbox"] {
    width: 20px;
    height: 20px;
    cursor: pointer;
    accent-color: var(--primary-color);
}

.setting-label span {
    font-size: 0.95rem;
    color: var(--text-primary);
}

.sync-info {
    font-size: 0.85rem;
    color: var(--text-secondary);
    margin: 15px 0;
}

.input-section {
    margin-bottom: 20px;
}

.todo-form {
    display: flex;
    gap: 10px;
    background: var(--card-bg);
    padding: 15px;
    border-radius: var(--radius);
    box-shadow: var(--shadow);
}

#todoInput {
    flex: 1;
    padding: 12px 16px;
    border: 2px solid var(--border-color);
    border-radius: 8px;
    font-size: 1rem;
    transition: var(--transition);
    outline: none;
}

#todoInput:focus {
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(52, 152, 219, 0.2);
}

#todoInput::placeholder {
    color: #aaa;
}

.btn {
    padding: 12px 24px;
    border: none;
    border-radius: 8px;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: var(--transition);
}

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

.btn-primary:hover {
    background: var(--primary-dark);
    transform: translateY(-2px);
    box-shadow: var(--shadow);
}

.btn-secondary {
    background: var(--bg-color);
    color: var(--text-primary);
    padding: 10px 20px;
    font-size: 0.9rem;
}

.btn-secondary:hover:not(:disabled) {
    background: var(--border-color);
}

.btn-secondary:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

.btn-danger {
    background: transparent;
    color: var(--danger-color);
    padding: 8px;
    font-size: 1.2rem;
}

.btn-danger:hover {
    background: rgba(231, 76, 60, 0.1);
}

.filters-section {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 20px;
    flex-wrap: wrap;
    gap: 10px;
}

.filter-buttons {
    display: flex;
    gap: 8px;
}

.filter-btn {
    padding: 8px 16px;
    border: none;
    background: var(--card-bg);
    border-radius: 20px;
    font-size: 0.9rem;
    cursor: pointer;
    transition: var(--transition);
    color: var(--text-secondary);
}

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

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

.stats {
    font-size: 0.9rem;
    color: var(--text-secondary);
    background: var(--card-bg);
    padding: 8px 16px;
    border-radius: 20px;
}

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

.todo-item {
    display: flex;
    align-items: center;
    gap: 15px;
    padding: 15px 20px;
    background: var(--card-bg);
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    transition: var(--transition);
    animation: fadeIn 0.3s ease;
}

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

.todo-item:hover {
    box-shadow: var(--shadow-hover);
    transform: translateY(-2px);
}

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

.todo-checkbox {
    width: 24px;
    height: 24px;
    border: 2px solid var(--border-color);
    border-radius: 6px;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: var(--transition);
    flex-shrink: 0;
}

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

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

.todo-checkbox.checked::after {
    content: '✓';
    color: white;
    font-size: 14px;
    font-weight: bold;
}

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

.todo-date {
    font-size: 0.75rem;
    color: var(--text-secondary);
    margin-right: 10px;
}

.todo-actions {
    display: flex;
    gap: 5px;
    opacity: 0;
    transition: var(--transition);
}

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

.empty-state {
    text-align: center;
    padding: 60px 20px;
    display: none;
}

.empty-state.visible {
    display: block;
}

.empty-icon {
    font-size: 4rem;
    margin-bottom: 20px;
}

.empty-state p {
    color: var(--text-secondary);
    font-size: 1.1rem;
}

.empty-hint {
    font-size: 0.9rem !important;
    margin-top: 10px;
}

.notification {
    position: fixed;
    bottom: 20px;
    left: 50%;
    transform: translateX(-50%) translateY(100px);
    background: var(--text-primary);
    color: white;
    padding: 15px 30px;
    border-radius: 10px;
    box-shadow: var(--shadow-hover);
    opacity: 0;
    transition: var(--transition);
    z-index: 1000;
}

.notification.visible {
    transform: translateX(-50%) translateY(0);
    opacity: 1;
}

.notification.success {
    background: var(--success-color);
}

.notification.error {
    background: var(--danger-color);
}

.notification.warning {
    background: var(--warning-color);
}

@media (max-width: 600px) {
    .app-container {
        padding: 15px;
    }

    .app-header {
        flex-direction: column;
        gap: 15px;
        text-align: center;
    }

    .todo-form {
        flex-direction: column;
    }

    .filters-section {
        flex-direction: column;
        align-items: stretch;
    }

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

    .stats {
        text-align: center;
    }

    .todo-actions {
        opacity: 1;
    }
}