Created attachment 421951 [details] Test case Check the attached example. There is a 1 pixel difference between the second and the other two examples just between the bottom red and green borders. There is no difference in the rendering in both Firefox and Chromium. They render the three "columns" as WebKit renders the second one, i.e, with 1 pixel between the two borders. I'm almost sure it's a rounding issue due to using sizes with decimals, because it does not happen when you use natural numbers instead of real ones.
Created attachment 421952 [details] Screenshot Adding a screenshot demonstrating the issue.
<rdar://problem/75221421>
I am not able to reproduce this bug in Safari 16.1 and Safari is matching other browsers (Chrome Canary 109 and Firefox Nightly 108) and showing "gap" similar to middle one from reference screenshot for all in all browsers. Marking this as "RESOLVED CONFIGURATION CHANGED", please reopen if it is reproducible with updated test case. Thanks!