Safari renders black lines in between divs on my website at some scales. It is particularly bad when it breaks apart an image that is chopped in two different divs for a but
The following CSS, added to the problematic div with a specified background-image, is what fixed it for me. Anything less than 3px would still show light artifacts at some Safari zoom levels.
margin-top: -3px; /* for Mobile Safari dark line artifact */
padding-top: 3px; /* for Mobile Safari dark line artifact */