.menu {
    display: flex;
    list-style: none;
    background: blue;
}

.menu li {
    position: relative;
}

.menu a {
    color: white;
    padding: 12px 20px;
    display: block;
    text-decoration: none;
    border-right: 1px solid white;
}

.menu a:hover {
    background: oldlace;
    color: black;
}

.submenu {
    display: none;
    position: absolute;
    top: 100%;
    left: 0;
    list-style: none;
}

.dropdown:hover .submenu {
    display: block;
}

.submenu a {
    background: blue;
}