Fix Theme bug in Safari

I found my new theme behaves strange in iOS. After an inspect, I found this was caused by missing the vendor prefix of some css property.

From I know that the 3d transform property although is supported by Safari and iOS, but it is still needed a vendor prefix to make it work. After add the -webkit- prefix. the bug on iOS disappeared. For convenience, I using a grunt task grunt-autoprefixer to do this automatically.