* Fixes position of the top arrow, and border width of both
* Merged top and transform properties
* .5px values are required to make arrow border appear the same with as overall popover border width
I did have a chance to try it out on a Windows machine with a non-high DPI display and there were no issues. And I just re-tested it with Firefox on macOS using the "Open in Low Resolution" option and it looked more or less ok (bearing in mind that it the whole app is then a blurry mess, and that using custom zoom levels causes the arrow to break slightly, but that was also the case on Firefox before this change)