Change background color for category list

I’m trying to make my category list have the background color change on hover.

I’ve tried using various methods including a:hover and transition but seem to missing something. The background colors aren’t responding to anything I’ve tried coding.

Here is a sample of what I currently have for each category link:

<h3 style="background-color:#853385;opacity: .8; text-align:center;"><a href="http://enduringepilepsy.com/category/awareness_advocacy/" >Awareness & Advocacy</a></h3>

I’d like them change to a grey color on hover. If anyone can offer input I’d appreciate the help.

enduringepilepsy.com