You may have heard that Moodle 3.5 will use Bootstrap 4 stable (rather than alpha). MDL-56511 has just been integrated and so we now need to check all over Moodle 3.5 dev for possible display problems when using the Boost theme.
If you have time, and would like to help with theme testing, please choose a test from the list of subtasks of MDLQA-11628 and click the 'Assign to me' link. Our QA testing site can be used to run the tests.
The tests work the same way as regular QA tests (as described in the QA testing guide). If you've not helped with QA testing before and would like to be involved, please send me a message and I'll add you to the testers group in the Moodle Tracker. New testers are always welcome.