I am using Joplin 2.7.13 (the latest version) on a laptop running Windows 10 Home, and I have a problem with the note editor (markdown).
I haven't used Joplin in a while, but I remember the note editor being in coloured monospace font. Now it looks the same as the font in the viewer panel.
I am really sorry for asking such a noob question, but I've been trying to solve the problem myself for the past few hours (playing with the appearance settings) and I've searched online for the answer, but I didn't find the answer I was looking for.
If you are on Windows make sure you have fully quit the app and not just minimised it to the systray.
If you have definitely done that then can you post the contents of your userchrome.css file here (put it in a code fence by surrounding in triple backticks (```))
That one works fine for me. Are you using the right theme for it? (i.e. to use that one you need to be using the dark theme, for the light theme you need to use a different set).
The userchrome.css css above should change colours and some styling, however setting the editor to use a monospace font again is done using Appearance in the settings menu. Just enter the name of a monospace font installed on your system.