Text editing in the CMS is painful because of three factors combined: 1) small font; 2) black background; 3) lines that are very long. I'd recommend to follow guidelines for good readability. A white background would be desirable but if not possible, at least a larger font and the possibility to resize the editor would help. Ideally I would not want to have more than 65 characters per line.
Trying to resize the font using the browser native functionality (cmd + +) does not work, since everything gets larger and some elements get cut off. The attached image is a screenshot of how I see it from my computer. Thanks