Calendar plugin - changing year/day color

Hi everyone— I’m trying to find a way to change the color of the day and year in the Calendar plugin by Liam Cain, since I can barely see them in my monitor.
Following the instructions on GitHub, I was able to make a .css custom file and change the background color pretty easily, although I’m still trying to figure out what part of the code refers to what I want to customize.
I’ve been stuck in the Inspect Element since yesterday— could someone please help me with this? TIA