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

body {
    font-family: Arial, sans-serif;
    padding: 30px;
    background-color: #f4f4f4;
}

#main-nav {
    list-style: none;
    width: 150px; 
    background-color: #000000; 
}

#main-nav li {
    position: relative; 
    border-bottom: 1px solid #FFF; 
}

#main-nav li a {
    display: block;
    padding: 12px 15px;
    text-decoration: none;
    color: #FFF; 
    font-size: 14px;
    transition: 0.3s;
}

#main-nav li:hover > a {
    background-color: darkgray;
}

#main-nav ul.sub-menu {
    list-style: none;
    position: absolute;
    top: 0; 
    left: 100%;
    width: max-content; 
    min-width: 150px;
    background-color: #000000;
    display: none;
    z-index: 100;
}

#main-nav li:hover > ul.sub-menu {
    display: block;
}

#main-nav ul.sub-menu li ul.sub-menu {
    display: none;
    left: 100%; 
    top: 0;
}

#main-nav ul.sub-menu li:hover > ul.sub-menu {
    display: block;
}

#main-nav ul.sub-menu li a {
    padding: 10px 15px;
    font-size: 13px;
    white-space: nowrap; 
}