On retina screens CSS pixels don’t match device (physical) pixels. A device pixel ratio of 2 means one CSS pixel equals two device pixels. Here are few ways to draw a one-device-pixel border. Half-pixel border border: 0.5px solid black; Cons: Works only in Firefox and Safari 8 (introduced in OS X Yosemite). border-image border-width: 1px; border-image: url(border.gif) 2 repeat; border.gif is a 6×6