WordPress 5 was recently released. One of the first things I noticed was the new editor. There appeared to be lots of features, but there was one a huge issue for me. The post or page text area is very tiny on large screens. This is due to a div being locked at a fix width. I guess the people at WordPress believe everyone uses laptops or smaller devices. But for the developer like myself I use a very large screen.
You can easily fix this by installing the module Admin CSS MU. Then you just need to add the following CSS:
I also noticed that the new editor is also buggy. So if you get too frustrated, you can always install the classic editor.