@AliAS remember after locating and fixing the error to hit ctrl + o to save and ctrl + x to exit nano.

Thanks to both of you for the quick replys. As I said, I’m very new but learning quickly. After seeing Mykel’s post (sorry if I’m spelling that incorrectly as I cannot see the post while typing a reply on my android) I reopened the custom.css file and noticed I made a syntax error. I replaced the colon after yellow with a semicolon and I was good to go.

Another suggestion, and someone please correct me if I am wrong, you could delete the config.js file and save as or copy the config-sample.js as a new config.js file. That way you have a functioning config.js. But doing so, you would have to reconfigure all your modules. Does that sound right?