v4: hidden-xs-down mismatch with hidden-sm-up

[wnr]

There's one pixel between xs-down and sm-up that makes the following case not working as expected:

<div class="hidden-xs-down hidden-sm-up">...</div>

Expected is that the div will never be visible.

If font size is 16px, the div will be visible at 543 px.

sm: 16*33.9 = 542.4 px
sm: 16*34 = 544 px

This same error occurs with hidden-sm-down hidden-md-up, etc.

[cvrebert]

As of #17403, we now use pixels instead of ems, which should fix this problem.
Please re-test against current the v4-dev branch. Happy to reopen this if some variation of the problem still exists.