Changing color when hovering over icons

Hi, I'm trying to change the colour when you hover over icons (like the "rocket" and other icons on the front page). It's currently orange, but I've tried changing it to blue or red and it doesn't seem to work.

I have override.css enabled in the template settings and I put this into the css code box there:

gkFeatures > a:hover { background: blue; }

And nothing happens when I save and then refresh the page, it doesn't change. What am I doing wrong?

I think the problem is Override.css just isn't working for me! None of the changes I've done in override.css show on the webpage.

I can change the modules and everything, but the Override.css enabled just doesn't seem to work. I've tried putting in code directly into the override.css file and also into the "custom css code" box in the template manager, but neither works for me. Any ideas?