I hate to open an unclear/ambiguous issue, but I've been unable to track down what's actually going wrong here.
With the following CSS, simply running css.parse() is blowing up:

Error: undefined:1:249: property missing ':'

It seems to only be occurring when there are multiple rules on one line (i.e. minified) that contain the string "charset", only when the SVG is URL encoded. I've stripped it down as much as I can to get it to a readable size (original file: http://www.shopify.com/assets2/application-bf82c00b0b5b610626f416a6ccc3d6aa.css).

Any thoughts on what might be going on here? I'll try to take a closer look in the next few days but figured I'd open the issue in the meantime. Thanks!

.thing1{background-image:url("data:image/svg+xml;charset=utf8,%3Csvg%3E%3Cg%3E%3Crect%20transform=%22matrix(0.7071%20-0.7071%200.7071%200.7071%20-9.5016%2021.7357)%22/%3E%3C/g%3E%3C/svg%3E");}.thing2{background-image:url("data:image/svg+xml;charset=utf8,%3Csvg%3E%3C/svg%3E");}