I've been having this problem, which makes it terribly difficult to mark students' work with a rubric, as there's no way to resize the rubric box. Our IT are'nt very helpful and we can't make any modifications to Moodle or add any plug-ins. But I finally figured out a rough work-around solution, which I thought might help someone else in this situation.
The problem:
Lots of space on either side of the student's submission, but only about a third of the rubric is showing!
To fix it, at least temporarily: Go to Tools > Browser Tools > Web Developer Tools (this is on Firefox, but it shouldn't be too difficult to figure it out on other browsers)
This window will appear. First, click the little arrow in a box (circled) in the top left of the window. Then, click on the section of the page outlined in purple that the arrow's pointing to. Make sure it's this exact section, or it won't work. There are a lot of similar-looking ones, right nearby.
Go to the middle section, of the Web Developer Tools window, and scroll down until you see this:
Then, all you need to do is change 'left: 70%' to 'left: 50%' and width 30%' to 'width 53%'. Those are the numbers that worked for me, but it'll depend on how wide your rubric is and the size of your screen, etc. Some settings (like 'width 50%') resulted in an unusable set-up, but for some reason 53% worked. People who actually know what is going on could perhaps comment to explain?
Here's the final outcome:
The important thing to remember is that, no matter what you do, you can't 'break' the page. If it all goes to hell, just refresh the page and it'll be back to normal!
The new settings will stay put when you choose 'save and show next', pick another user from the 'change user' dropdown, or change the filtering of submissions. But it'll revert to the normal settings if you refresh the page or close and reopen it. But once you have the hang of it, it's quick and easy to fix it again.
Hope this helps someone struggling like I was!
