Right now XenForo adds many prefixes that are not required by modern browsers. Including prefixes for: border-radius box-shadow box-sizing According to caniuse.com statistics we don't need any of these prefixes anymore. I suggest removing them, making css file lighter. Otherwise, there is an excellent alternative called Autoprefixer. Yes, it's written in coffeescript and it's a plugin for PostCSS (which is in JS), but there's a PHP version of that plugin, which may improve prefixing process a lot. You can even set your browser support table!