Oprea

Changing the menu buttons in the header is easy (in fact it is easy and the same anywhere because it is an object and is the same/can be copied anywhere)

Template/Template Content, double click on menu object.

Now simply change whatever you want.

(so once you have it as you wish, you can even copy it (right click copy) and paste it else where (eg sticky bar).

Based on your screen shots, please ensure the the menu object is totally within the header (allowing the menu object to expand beyond the header "boundaries" results in unexpected consequences)