Yeah CodePen is not good example of IDE but it's example of good UX. As example of real IDE check stackblitz.com/ it have file tree on the left, worse UX is to surprise the user, every IDE out there have file tree on the left. If open in new tab is for multiple screen you should make it optional maybe dropdown menu (with 3 dots) near the opened file.
Yeah CodePen is not good example of IDE but it's example of good UX. As example of real IDE check stackblitz.com/ it have file tree on the left, worse UX is to surprise the user, every IDE out there have file tree on the left. If open in new tab is for multiple screen you should make it optional maybe dropdown menu (with 3 dots) near the opened file.
Thanks, that's very useful. I agree with all your points. Clearly I'm not a UX/UI person myself 😃