Create "hover" effect over Thumbnails

Hi,
Theme: F8-Light
Website: https://www.somewhereny.com

I am using “featured Image” to display a single 300px by 300px image to define each post on my homepage. As I am creating an e-commerce website I want each Image, when ‘hovered’ over to darken and display text. I know how to do this using the ‘hover’ function, but I dont know how to do it using ‘featured image’ function.

Here is a screen-grab much like what I am trying to do, notice the item darkened is being ‘hovered’ over with the mouse.

Thanks!