Created attachment 206415 [details] drop shadow with offset x and y 0 on element with rounded corners When applying a filter drop-shadow with offset x, y and blur 0 but drop-shadow color rgb(255,0,0) or any other color on an element with border radius the color for the drop-shadow shows like a border around the element.
Safari, Chrome, and Firefox all agree on rendering for this test case. I don't believe there is any remaining compatibility issue.