:root {
    --nav-width: 200px;
    --nav-bg-color: #333;
    --nav-hover-color: #555;
    --nav-text-color: white;
    --dropdown-bg-color: #444;
}

.navbar {
    position: fixed;
    top: 0;
    left: 0;
    height: 100%;
    width: var(--nav-width);
    background-color: var(--nav-bg-color);
    color: var(--nav-text-color);
    padding-top: 20px;
    z-index: 100;
}

.navbar ul {
    list-style-type: none;
    padding: 0;
    margin: 0;
}

.navbar li {
    position: relative;
}

.navbar a {
    display: block;
    color: var(--nav-text-color);
    text-align: left;
    padding: 14px 16px;
    text-decoration: none;
    cursor: pointer;
    transition: background-color 0.3s;
}

.navbar a:hover {
    background-color: var(--nav-hover-color);
}

.dropdown-content {
    display: none;
    background-color: var(--dropdown-bg-color);
    width: 100%;
    box-shadow: 0px 8px 16px 0px rgba(0, 0, 0, 0.2);
}

.dropdown-content a {
    padding: 12px 16px;
}

.dropdown:hover .dropdown-content {
    display: block;
}

/* 调整主内容区域的边距，为导航栏留出空间 */
body {
    margin-left: var(--nav-width) !important;
    padding-left: 20px !important;
}