Safari showing border of transparent PNG
I just faced the same issue and stumbled upon this question.

For me, the image showed a thin, medium-dark, shadowy border at the edge between the non-transparent and the transparent part of the image.
The issue was only visible in Safari.



For me, the solution was to simple add transform: translateZ(0px) to the image. This changes the rendering of the image in a way that prevents the border.



However, you might want to restrict this fix to Safari since it causes the image to be rendered pixelated in Chrome.