Vendor prefix mixing

Since Bootstrap 4 relies on a tool called Autoprefixer to automatically add vendor prefixes to CSS rules, the vendor prefix mixins which were marked as deprecated in Bootstrap version 3.2 have now been completely removed. In addition, the following mixins have also been removed (source: Bootstrap 4 documentation—https://getbootstrap.com/docs/4.0/migration/):

animation, animation-delay, animation-direction, animation-duration, animation-fill-mode, animation-iteration-count, animation-name, animation-timing-function, backface-visibility, box-sizing, content-columns, hyphens, opacity, perspective, perspective-origin, rotate, rotateX, rotateY, scale, scaleX, scaleY, skew, transform-origin, transition-delay, transition-duration, transition-property, transition-timing-function, transition-transform, translate, translate3d, and user-select