CSS Calc的替代品()?小于或SASS能对像素计算做百分比吗?

I've been looking for a while for a way to do percent to pixel calculations without using calc(). I'd love to be able to use calc but currently mobile safari (ios) does not support it before ios6. Is there a way to do this in LESS? I know you can do calculations but as far as I can tell you cant do something like 100% - 20px. Any suggestions?I've been looking for a while for a way to do p