In the footer menu I can inspect the transition but I cannot see the transition colour to change it.

I have been asked to create a page with css / html from a design.
Here is the design bg image
Preview Image

I’m trying to apply a text-decoration-color transition effect to a child element of a link. Here’s a sample of that markup:

I have an “a” element which works like a button, it has a background picture. I need the background picture to become slightly bigger on :hover with 0.3 second transition. The background picture changes, but there is no animation, it always works instantly no matter what I do. So the transition effect is broken for some reason, but why?