It’s probably better not to add that code to Events Calendar PRO but rather to set it up as a custom stylesheet. This is very much the domain of custom development, but why not check out the following resource from the WordPress documentation and see if that gets you on track:
Hi, Lori. As it’s been over two weeks since your last reply, I’m going to close this thread. Please open a new one if you choose to pursue this further in the future.