I’ve not had a chance to put together a PR for this, but I’ve fixed it on my own site with custom CSS for now:
.admin-nav {
position: static;
float: none;
width: 100%;
font-size: 80%;
margin: 0;
}
.admin-nav .nav-stacked {
display: flex;
flex-wrap: wrap;
}
.nav-stacked li {
padding: 0;
margin: 0;
}
.nav-stacked li a {
padding: 5px 10px;
font-size: 100%;
line-height: auto;
}
.nav-stacked .active > a::after, .nav-stacked li > a.active::after {
content: none;
}
.admin-detail {
padding: 0;
}
…which produces something like this:
