They also point out that substantial performance gains are given by using 'will-change,' as in the following. .app-menu { -webkit-transform: translateX(-100

They also point out that substantial performance gains are given by using 'will-change,' as in the following. .app-menu { -webkit-transform: translateX(-100%); transform: translateX(-100%); transition: transform 300ms linear; will-change: transform; } And I'd point out that the authors are specifically stating that animating transform+opacity (via a 'transition') are more efficient than things like left, top, bottom, etc.—because those properties affect the layout stage, which is earlier than the composite stage (where the transform+opacity properties operate), and subsequent stages have to be recalculated. They also discuss different ways of structuring DOM trees to create the same animation which have performance trade-offs.