Along the same line and I need direction here or where I should look for assistance.

I use latest Joomla and Protostar Template. I have created side menus and use images rather than text.
I want the image to change to another image on mouseover.

Should I make this happen through editing template.css or adding to my user.css?
I see in the template Under >Menu and then the Edit Item >Link Type tab, "Image CSS Style".
I cannot find any clarification as to how this should be used or if it might be the way I can accomplish my goal.

If someone knows the actual code that would be appreciated.

Hello,

These links will help you
docs.joomla.org/Understanding_Joomla!_templates
getk2.org/documentation/tutorials/174-templating-with-k2-and-the-concepts-of-sub-templates