A user reported a bug in our theme, which turned out to be due to the use of the bootstrap class m-x-1 on some element.
That is implemented as
So basically it is impossible to override. This is pretty much as bad as putting style="margin-left: 14px; margin-right: 14px" in the HTML, which would not be allowed. Boostrap docs here: https://getbootstrap.com/docs/4.1/utilities/spacing/
If the goal of the UI team is to improve Moodle's HTML and CSS, then this has not place n Moodle. We should ban it in the coding style, and make a codechecker rule to detect it.