Clean / Bootstrap theme: Categories & Items page may be too wide to be usable

To reproduce:

Go to a course with lots of grade items, and at least one category or item with a long name.
Go to the gradebook Categories and Items page.
Note that the action icons are off the right edge of the screen.
Scroll to the bottom of the page, then scroll right to access the icons.
Now the activity names on the left are not visible.

This makes managing grade categories and items really clunky, if not impossible, for those courses with a lot of items.