z-index problem

I have the same issue, but I do not believe the plugin is actively developed any more, so doubt whether a reply from the developer will be forthcoming ??

I fixed it myself with some css
add this to your custom css:

.overlay ul li {
display: none;
height: 20%;
height: calc(100% / 5);
min-height: 54px;
}

.open.overlay ul li {
display: block;
}

Let’s update this plugin ourself ??
some extra css to make the links animate!

li {
display: inline-block;
position: relative;
padding-bottom: 3px;
margin-right: 10px;
}
li:last-child {
margin-right: 0;
}

li:after {
content: ”;
display: block;
margin: auto;
height: 3px;
width: 0px;
background: transparent;
transition: width .5s ease, background-color .5s ease;
}
li:hover:after {
width: 100%;
background: #fff;
}