How to make Mhmm compliant with accessibility standards

You can achieve this with a few lines of CSS.

Technically you can navigate the header via keyboard however there just aren’t focus styles in place to show which anchor is selected.

You need to add CSS similar to this to achieve the same.,
#mhmm a:focus,
#mhmm-menu-layout-loader a:focus {
border: 2px solid black;

The exact code will change depending on your menu, but this is a good starting point.

Thanks to Cameron Ramaekers.