background-2x() mixin
background-3x() mixin
inset-shadow() mixin
box-sizing() mixin
Add overflow: hidden; to rounded() mixin
Add overflow: hidden; to border-radius() mixin
Change name of rotate() mixin to transform-rotate()
Add unprefixed attribute to transform-rotate() mixin
Add transform-scale() mixin
Add transform-translate() mixin
Add transform-skew() mixin
TODO: Tackle transform-matrix() mixin