:root {
    --primary-color: #4CAF50;
    --secondary-color: #2196F3;
    --success-color: #4CAF50;
    --warning-color: #FF9800;
    --danger-color: #F44336;
    --text-primary: #333;
    --text-secondary: #666;
    --bg-light: #f5f5f5;
    --bg-white: #fff;
    --border-color: #ddd;
    --shadow: 0 2px 8px rgba(0,0,0,0.1);
    --shadow-lg: 0 4px 12px rgba(0,0,0,0.15);
}

body {
    font-family: 'PingFang SC', 'Microsoft YaHei', sans-serif;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    min-height: 100vh;
    padding: 1rem;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
}

/* 头部 */
.header {
    background: var(--bg-white);
    border-radius: 16px;
    padding: 1.5rem;
    margin-bottom: 1.5rem;
    box-shadow: var(--shadow-lg);
}

.header-content {
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: 1rem;
}

.header h1 {
    font-size: 1.8rem;
    color: var(--primary-color);
    margin: 0;
}

.header-actions {
    display: flex;
    gap: 1rem;
    align-items: center;
}

.date-picker-wrapper {
    position: relative;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.date-display {
    font-size: 1rem;
    color: var(--text-secondary);
    padding: 0.5rem 1rem;
    background: var(--bg-light);
    border-radius: 8px;
    cursor: pointer;
    transition: all 0.3s;
}

.date-display:hover {
    background: #e8e8e8;
}

.date-picker {
    padding: 0.5rem;
    border: 2px solid var(--border-color);
    border-radius: 8px;
    font-size: 0.9rem;
    cursor: pointer;
    transition: border-color 0.3s;
}

.date-picker:focus {
    outline: none;
    border-color: var(--primary-color);
}

/* 按钮 */
.btn {
    padding: 0.6rem 1.2rem;
    border: none;
    border-radius: 8px;
    font-size: 1rem;
    cursor: pointer;
    transition: all 0.3s;
    font-weight: 500;
}

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

.btn-primary:hover {
    background: #45a049;
    transform: translateY(-2px);
    box-shadow: var(--shadow);
}

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

.btn-secondary:hover {
    background: #0b7dda;
}

.btn-danger {
    background: var(--danger-color);
    color: white;
    padding: 0.4rem 0.8rem;
    font-size: 0.9rem;
}

.btn-danger:hover {
    background: #da190b;
}

/* 主内容区 */
.main-content {
    background: var(--bg-white);
    border-radius: 16px;
    padding: 2rem;
    box-shadow: var(--shadow-lg);
    min-height: 500px;
}

.view {
    display: none;
}

.view.active {
    display: block;
}

/* 统计卡片 */
.stats-cards {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 1.5rem;
    margin-bottom: 2rem;
}

.stat-card {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
    padding: 1.5rem;
    border-radius: 12px;
    text-align: center;
    box-shadow: var(--shadow);
}

.stat-card:nth-child(2) {
    background: linear-gradient(135deg, #4CAF50 0%, #45a049 100%);
}

.stat-card:nth-child(3) {
    background: linear-gradient(135deg, #FF9800 0%, #F57C00 100%);
}

.stat-number {
    font-size: 2.5rem;
    font-weight: bold;
    margin-bottom: 0.5rem;
}

.stat-label {
    font-size: 1rem;
    opacity: 0.9;
}

/* 表单 */
.add-homework-form {
    background: var(--bg-light);
    padding: 2rem;
    border-radius: 12px;
    margin-bottom: 2rem;
}

.add-homework-form h2 {
    margin-top: 0;
    margin-bottom: 1.5rem;
    color: var(--primary-color);
}

.form-group {
    margin-bottom: 1.5rem;
}

.form-group label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 500;
    color: var(--text-primary);
}

.form-group input,
.form-group select,
.form-group textarea {
    width: 100%;
    padding: 0.75rem;
    border: 2px solid var(--border-color);
    border-radius: 8px;
    font-size: 1rem;
    transition: border-color 0.3s;
}

.form-group input:focus,
.form-group select:focus,
.form-group textarea:focus {
    outline: none;
    border-color: var(--primary-color);
}

/* 过滤栏 */
.filter-bar {
    display: flex;
    gap: 1rem;
    margin-bottom: 1.5rem;
    flex-wrap: wrap;
}

.filter-input {
    padding: 0.6rem;
    border: 2px solid var(--border-color);
    border-radius: 8px;
    font-size: 1rem;
}

/* 作业列表 */
.homework-list {
    display: flex;
    flex-direction: column;
    gap: 1rem;
}

.homework-item {
    background: var(--bg-white);
    border: 2px solid var(--border-color);
    border-radius: 12px;
    padding: 1.5rem;
    transition: all 0.3s;
    display: flex;
    align-items: flex-start;
    gap: 1rem;
}

.homework-item:hover {
    border-color: var(--primary-color);
    box-shadow: var(--shadow);
    transform: translateY(-2px);
}

.homework-item.completed {
    opacity: 0.7;
    background: #f9f9f9;
}

.homework-checkbox {
    width: 24px;
    height: 24px;
    cursor: pointer;
    flex-shrink: 0;
    margin-top: 0.25rem;
}

.homework-content {
    flex: 1;
}

.homework-subject {
    display: inline-block;
    padding: 0.25rem 0.75rem;
    background: var(--primary-color);
    color: white;
    border-radius: 20px;
    font-size: 0.85rem;
    margin-bottom: 0.5rem;
    font-weight: 500;
}

.homework-text {
    font-size: 1.1rem;
    color: var(--text-primary);
    margin-bottom: 0.5rem;
    line-height: 1.6;
}

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

.homework-meta {
    font-size: 0.85rem;
    color: var(--text-secondary);
    display: flex;
    gap: 1rem;
    flex-wrap: wrap;
}

.homework-notes {
    font-size: 0.9rem;
    color: var(--text-secondary);
    font-style: italic;
    margin-top: 0.5rem;
}

.homework-time {
    display: inline-flex;
    align-items: center;
    gap: 0.3rem;
    font-size: 0.9rem;
    color: #e65100;
    background: linear-gradient(135deg, #fff3e0 0%, #ffe0b2 100%);
    padding: 0.4rem 0.9rem;
    border-radius: 16px;
    font-weight: 600;
    margin-top: 0.6rem;
    border: 1px solid #ffcc80;
    box-shadow: 0 2px 4px rgba(230, 81, 0, 0.1);
}

.homework-actions {
    display: flex;
    gap: 0.5rem;
    flex-shrink: 0;
}

/* 空状态 */
.empty-state {
    text-align: center;
    padding: 3rem 1rem;
    color: var(--text-secondary);
}

.empty-state-icon {
    font-size: 4rem;
    margin-bottom: 1rem;
}

.empty-state-text {
    font-size: 1.2rem;
}

/* 通知 */
#notificationContainer {
    position: fixed;
    top: 20px;
    right: 20px;
    z-index: 1000;
}

.notification {
    background: var(--bg-white);
    padding: 1rem 1.5rem;
    border-radius: 8px;
    box-shadow: var(--shadow-lg);
    margin-bottom: 0.5rem;
    display: flex;
    align-items: center;
    gap: 0.75rem;
    min-width: 300px;
    animation: slideIn 0.3s ease;
}

@keyframes slideIn {
    from {
        transform: translateX(400px);
        opacity: 0;
    }
    to {
        transform: translateX(0);
        opacity: 1;
    }
}

.notification.success {
    border-left: 4px solid var(--success-color);
}

.notification.error {
    border-left: 4px solid var(--danger-color);
}

.notification.info {
    border-left: 4px solid var(--secondary-color);
}

/* 响应式 */
@media (max-width: 768px) {
    .header h1 {
        font-size: 1.4rem;
    }
    
    .stats-cards {
        grid-template-columns: 1fr;
    }
    
    .homework-item {
        flex-direction: column;
    }
    
    .homework-actions {
        width: 100%;
        justify-content: flex-end;
    }
    
    .filter-bar {
        flex-direction: column;
    }
    
    .filter-input {
        width: 100%;
    }
}