Context types where role may be assigned check boxes incorrectly displayed in Boost

This issue only affects Moodle 3.5 sites using the Boost theme (not 3.4.2 sites).

1. Log in as an admin or manager and go to Define roles in the Site administration.
   Click the 'Add a new role' button, leave "Use role or archetype' set as 'No role' and click the continue button.
2. On the Add a new role page, look at the setting 'Context types where this role may be assigned'.

Expected result: Check boxes are listed vertically.

Actual result: Check boxes are listed horizontally with no spacing.

Check boxes using Boost:

Check boxes using Clean:

(Note that in Clean the alignment isn't quite right.)