CSS Bug in Chrome, Safari, Vivaldi

The bug has been found in these browsers:

The bug does not appear in these browsers:

Description of the bug:

The table cells containing 4 and 5 get rendered with a heavy (3px red) border-bottom, but the CSS specifies just plain "1px solid #bbb".

If the "bot" class is removed from the cell containing 3, then the problem goes away.

The border-top of the cells containing 4 and 5 seems not to be affected by the bug.

A 1234?5? 678910
B 26 9

This bug has been reported to WebKit Bugzilla.

Valid CSS!

First version: 15-Nov-2016 Updated: 12-Dec-2018