Is there a SASS extension that would take SASS stylesheets, find neutral properties (e.g. border-radius) and output all vendor-specific properties for it (e.g. -webkit-border-radius etc) automatically?
I don't really want to create all the mixins manually nor write the code manually. I'm sure there must be such an extension, but I can't find it. Help?
There is a very nice gem that would fit your needs. It's called Bourbon
It will not replace your css with the vendor-specific one as it works as SASS is made to work.
It is basically a mixin collection that generates the cross-browser css properly.