CSS Classes for Main Navigation

Can they be used with this theme? If so, how do I go about defining them in the CSS Classes. I have my own set of icons that I will be uploading to my root domain. Thanks for the help

 

You can edit theme current css through
Appearance > Editor / style.css
And search for "menu".
You can provide image address through root domain or through media library.

 

I tried to do this, but am not sure how to write the code exactly in it. Any thoughts?

 

Please explain your issue where you want to make changes in your website, We will provide you CSS code for that and also share the link of your website.