Open: data:text/html,<div style="width:100px;height:100px;border:5px double green"></div> The corners don't render solidly. The code is rendering each line separately, when they could be rendering two boxes separately. <rdar://problem/16138952>
Created attachment 462414 [details] Safari Technology Preview 153 differ from other browsers I changed the test case into JSFiddle: Link - https://jsfiddle.net/nxucm9et/show and get following as above. It seems that the pixels are not interacting with each other and have one line in it. It is still reporducible.