#mainMenu{
    height: auto;
}
#mainMenu>ul>li:hover, #mainMenu>ul>li.active{
    border: none;
}
#mainMenu>ul>li:hover::after{
    position: absolute;
    content: '';
    left: 0;
    right: 0;
    bottom: 0;
    height: 3px;
    background-color: #000;
}