I'm trying to add some custom CSS to dictate a very small part of a plugin's look. I don't want to dequeue the whole think (I don't think) as I'm happy with the rest of it.
I found this answer here which would appear to be exactly what I need: https://wordpress.stackexchange.com/a/101038/118037
However I'm new to WP and I have not even the faintest idea of where I would put that second lot of code.
get_template_directory_uri() . '/mystyles.css',
Can anyone point me in the right direction?