Color of Read-More buttons in Post Grids

Hi there, I can’t figure out how to change the color and shape of the “Read more” buttons when inserting a post grid. The reference site: http://www.swissappetite.com

I would like to change these “red” buttons into my own custom color, and into a square.

Many thanks in advance for your help.

I’m using Highend Minimalistic demo as a basis.