Created by: Starsam80
I think screenshots show this change the best:
Before: 
After: 
.bd-* classes aren't in the regular bootstrap css, so when people copy these class names, they aren't going to do anything.
A small bug (but can be used as a feature) I noticed is when other class names appear after the bd-* class and they disappear as well, so something like <div class="d-flex bd-highlight p-2"> would display as <div class="d-flex">