Hi Sara,
Thanks for reaching out!
I took a look at the article you linked to, and it looks like it is a bit out of date – CSS files can no longer be overridden by copying them into your tribe-events folder (this only works for the front end calendar views – PHP files). I apologize for the misinformation there! I have flagged that article as being out of date so that we can get it updated.
However, you can add your CSS to the Additional CSS area under Appearance > Customize (if you have one) or to the style.css file of your child theme.
Can you try adding your CSS this way and see if that works?
Thanks,
Jennifer