Hi, can anyone suggest a script or let me know what sort of code should be used to achieve the same effect as this demo?

http://demo.joomshaper.com/extension...e-gallery.html

I do know how to use opacity in CSS to make an image darker or lighter on mouseover, but this looks like it's using javascript and it looks much slicker. I'd really like to have darkened images that light up on mouseover, but with that fade effect instead of just instantly changing like the opacity setting does. Any sugestions? Thanks!