How to add bar behind menu ?

greetings ,
I am using ample theme , i have tried very hard to get idea about how can i add a bar with some color behind menu titles ? my site is https://oneistoomuch.com/ , there as a menu title like home , privacy , about us , the background is just a white . what i want is to add some color behind that & to make it look like a bar. Also two menus moved down as i added menus. Can i make it all in a single colored bar with bold fonts ?
I am sorry , as i am a beginner & looking for your help.
every support will be much worthy for me.
Thanks