Hickory theme How to add hover img on social media icon?

Hi, I wanted to know how would I go about in changing the color/hover img of a social media icon like facebook on hover.

Something similiar to this site for example: https://lalomacd.com.mx/2013/

My current theme is hickory and the coding for the social media icon is in footer.php and style.css

I am having a hard time understanding how to keep the position the way they are while being able to create a hover img on them.