Horizontal Drop-Down Menu Not Working

Install a custom css plugin and add this CSS:

#nav,
#main,
#nav li {
    position: relative;
}

#nav ul li {
    height: auto;
}

#nav {
    z-index: 1;
    min-height: 56px;
}

#nav li ul {
    position: absolute;
    top: 100%;
    left: -999em;
    width: 100%;
}

#nav li ul:before {
    content: "";
    width: 100%;
    height: 10px;
    top: -10px;
    position: absolute;
    left: 0;
}

#nav li:hover ul {
    left: 0;
}

It’s a bit buggy on mobile. Try changing this:

#nav {
    z-index: 1;
    min-height: 56px;
}

To this:

#nav {
    z-index: 10;
    min-height: 56px;
}