Right now, when there is an error in the code other Thimble features are not available (for instance, clicking into tags to get help). If you are not a seasoned user, you wouldn't even know to look for errors as you try to remix the code. Even if you are seasoned, you are forced to scroll around away from where you are working to find it and it is not always visually striking. I would suggest some kind of alert that appears static at the top of the page, or scrolls with the window view, to help users navigate to the error.
NOTE that I kinda added a redundant bug: 967552