I tried your code on Chrome (Version 24.0.1312.57 m) with a 1680×1050 screen. When I flipped between your letter-spacing: 0.03em;
and letter-spacing: 0.0em;
it looked the same at default size, but when I zoomed in one level (CTRL +), the 0.03em text rendered wider than the 0.0em text.
So, I see several possible answers to your question:
- At default zoom level (CTRL 0), the 0.03em letter-spacing isn't wide enough to show any difference, but zoom level +1 (CTRL +) does show a difference.
- Maybe your down-level Chrome (17.0.963.79) doesn't handle sub-pixel
letter-spacing: [tiny]em;
as well as Chrome (24.0.1312.57 m) handles it. - Maybe your screen resolution isn't large enough to show a difference.