If you are looking for a media query, Chrome versions can be separated now. A while back I created this from research of combinations until I found a method that would work. I posted it months ago to browserhacks.com (I do testing for them). Chrome 29+ is targetable via media query. At this time, it is tested working in all modern versions of Chrome even development and Canary versions up to version 40.
Try this instead of the Chrome + Safari media query embedded in your mixin:
@media screen and (-webkit-min-device-pixel-ratio:0) and (min-resolution:.001dpcm) {
border-bottom: red;
}
There are live tests I have posted as well for this and others that I have worked on or created here:
http://browserstrangeness.bitbucket.org/css_hacks.html