.vertical-menu {
    width: 300px;
    /* Set a width if you like */
}

.vertical-menu a {
    transition: .5s;
    background-color: #eee;
    /* Grey background color */
    color: black;
    /* Black text color */
    display: block;
    /* Make the links appear below each other */
    padding: 5px;
    /* Add some padding */
    text-decoration: none;
    /* Remove underline from links */
    height: 35px;
    vertical-align: middle;
    font-family: sans-serif;
}

.vertical-menu a:hover {
    transition: .5s;
    background-color: #888;
    font-size: 18px;
    /* Dark grey background on mouse-over */
}

.vertical-menu a.active {
    background-color: #4CAF50;
    /* Add a green color to the "active/current" link */
    color: white;
}