How to apply filter only to parent element


I am trying to make it so that when I hover over each block the image gets darker but the text stays the same brightness. I applied this to my link blocks but unfortunately everything (including the child text) goes darker when I hover. How can I make it so that only the image gets darker on hover but the text stays the same colour?

Thank you!


Here is my public share link:
(how to access public share link)