#menu {
    list-style: none;
    padding: 0;
    margin: 0;
    width: 150px;
    background: #000000;
}

#menu li {
    position: relative;
    white-space: nowrap;
}

#menu li a {
    display: block;
    padding: 10px;
    color: #FFF;
    text-decoration: none;
    border-bottom: 1px solid #FFF;
}

#menu li a:hover {
    background: darkgray;
}

#menu li ul {
    display: none;
    position: absolute;
    top: 0;
    left: 150px;
    background: #000;
    width: max-content;
    list-style: none;
    padding: 0;
    margin: 0;
}

#menu li ul li ul {
    top: 0;
    left: 100%;
    width: max-content;
}

#menu li:hover > ul {
    display: block;
}