How to I change buttons within image blocks?

@peter

Someone recently answered my question regarding image blocks, and it was a great help! However, I am not unable to edit buttons that I've placed in those image blocks using the "link on button option" in the design tab. I would like to replace the button with a new icon without text and create a hover effect on that button within each image block. Does anyone know how to do this?

Here's the link to my site:

https://rabbit-gazelle-gbmt.squarespace.com/config/design/custom-css

The site is private. Can you setup an access password?

Also you should post this to Site Design and Styles category or Coding and Customization.