In clean, the drop zone in both the file picker and file manager has a border around it, in boost it does not. This causes a few problems with alignment and looking out of place. I avoided fixing in MDL-56910 because I wasn't certain on the intended direction. And the implication on the file manager, there is existing css there which has been styled for boost.

Steps to reproduce:

1. Go to course calendar
2. Go to Manage subscriptions page
3. Look at the Calendar file field in both enabled and disabled state (when calendar url is selected or file)