* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

#menu {
    list-style: none;
    width: 150px;
}

#menu li {
    position: relative;
}

#menu li a {
    display: block;
    width: 150px;
    padding: 10px;
    background: #000000;
    color: #FFFFFF;
    text-decoration: none;
    border-bottom: 1px solid #FFFFFF;
}

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

#menu li ul {
    display: none;
    position: absolute;
    top: 0;
    left: 100%; 
    width: max-content;
    list-style: none;
}

#menu li ul li ul {
    top: 0;
    left: 100%; 
}

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