The Back button is barely shown when requesting to join a subwiki

Preconditions: As Admin create a subwiki with the Membership Type "Any global user can request join but an admin must accept"

Steps to reproduce:

1. Login as simple user and go the Wiki index
2. Find the new Wiki in the list
3. Click "Request join"

Expected results: A message box appears where the user can motivate this join request followed by the Send Request and Back buttons.

Working on XWiki 13.10.6

Actual results: The buttons appear at the top of the message box, the Back button is barely shown without any text - the "Back" text appears at the bottom of the message box.