Main menu hover background color and bottom strip

How to change main menu hover background color and bottom strip?

This css use for changing black strip:

.l-header-horizontal #site-header .menu > li:before {
    background: #000 !important;
}

And this one for hover:

.l-header-horizontal #site-header .menu > li:after {
    background: #000 !important;
    opacity: 0.1 !important;
}

Change color and value of opacity for your taste.