.left-side {
    position: sticky;
    top: 0;
    height: calc(100vh - 60px);
    width: 200px;
    background-color: #f0f0f0;
    padding: 20px;
    overflow-y:auto ;
    margin-top: 50px;
}

.index {
    list-style-type: none;
    padding: 0;
}

.index li {
    margin-bottom: 10px;
}

.index a {
    text-decoration: none;
    color: #333;
    font-weight: bold;
}

.index ul {
    margin-top: 5px;
    margin-left: 15px;
}

.index ul li {
    margin-bottom: 5px;
}

.index ul a {
    font-weight: normal;
}