body {
    margin: 0;
    font-family: "Segoe UI", system-ui, sans-serif;
    background: linear-gradient(135deg, #f0f4ff, #e6eeff);
    color: #333;
    display: flex;
    height: 100vh;
    overflow: hidden;
}

/* 左侧导航 */
.sidebar {
    width: 220px;
    background: #1e293b;
    color: #fff;
    display: flex;
    flex-direction: column;
    padding: 20px;
    box-sizing: border-box;
}

.sidebar h2 {
    font-size: 18px;
    text-align: center;
    margin-bottom: 20px;
}

.nav-item {
    padding: 12px 16px;
    margin-bottom: 8px;
    cursor: pointer;
    border-radius: 8px;
    transition: background 0.3s;
}

.nav-item:hover,
.nav-item.active {
    background: #334155;
}

/* 右侧内容 */
.content {
    flex: 1;
    padding: 30px;
    overflow-y: auto;
}

.content-section {
    display: none;
    animation: fadeIn 0.4s ease;
}

.content-section.active {
    display: block;
}

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

    to {
        opacity: 1;
        transform: translateY(0);
    }
}

/* 弹窗 */
.modal-overlay {
    display: none;
    position: fixed;
    inset: 0;
    background: rgba(0, 0, 0, 0.4);
    justify-content: center;
    align-items: center;
}

.modal {
    background: white;
    border-radius: 12px;
    padding: 24px;
    width: 360px;
    box-shadow: 0 4px 16px rgba(0, 0, 0, 0.2);
    text-align: center;
}

.modal h3 {
    margin-top: 0;
}

.modal button {
    margin-top: 16px;
    padding: 8px 20px;
    border: none;
    background: #1e293b;
    color: white;
    border-radius: 6px;
    cursor: pointer;
    transition: 0.2s;
}

.modal button:hover {
    background: #334155;
}