Add missing css keywords / values

New keywords : `animation-delay` `animation-direction` `animation-duration` `animation-iteration-count` `animation-name` `background-size` `background-clip` `box-sizing` `overflow-x` `box-shadow` `opacity` `flex-flow` `resize` `align-content` `transform` `transition`

New values : `inherit` `content-box` `border-box` `table` `flex` `row` `wrap` `space-around` `infinite` `linear` `linear-gradient` `rgba` `webkit-box` `scale` `rotate` `translate` `translateX` `translateY` `skewX` `skewY`

Don't know how to add `@keyframes` and prefixes like `-webkit-`, `-moz-`, etc... :(