Internet Explorer (6,7,8) can mangle your
anti-aliasing when the ActiveX opacity filter
is applied to a floating object like this.
(note: screen cap was taken in IE 6 on Windows XP with "ClearType" anti-aliasing mode in effect. Results will vary by system.)
DANGEROUS CSS COMBINATION:
* Note that if any alpha is defined (100 is just an example), it will trigger error.
It turns out that IE is confused about which background color it should anti alias against.
Seems to choose black in this case. If we explicitly define a background-color, the rendering issue goes away.