.fade { opacity: 0; transition: opacity .15s linear; &.in { opacity: 1; } } .collapse { display: none; &.in { display: block; } // tr&.in { display: table-row; } // tbody&.in { display: table-row-group; } } .collapsing { position: relative; height: 0; overflow: hidden; transition-timing-function: ease; transition-duration: .35s; transition-property: height; }