How to add/show a colour border and underline to categories and subcategories in header, when hovering upon them?

[mendoh]

 

Hi everybody.

I am having difficulties in getting a hold of the very many graphic design features and elements available. 

I could not add a colour border and underline to the header (categories and) subcategories when I hover upon them, as shown in red on the top left of the picture (below). What I get during hovering is what you see on the top right side of the below picture. Could you point me out on how to customize it, so that it appears with the red highlights shown on the left when hovering?

Also, I have noticed that while the same header categories have been customized in their outlook and retain all their outlook customizations on the website homepage, as soon as I click on a category/sub-category, the same header categories appear as if they had never been customized at all, whenever the whole category/sub-category page is displayed (please see the below example).

Why is that happening and how to fix the issue?

Thank you