.fade {
  opacity: 0;
  -webkit-transition: opacity .15s linear;
       -o-transition: opacity .15s linear;
          transition: opacity .15s linear;
}
.fade.in { opacity: .75; }

.collapse { display: none; }
.collapse.in { display: block; }

.collapsing {
  position: relative;
  height: 0;
  overflow: hidden;
  -webkit-transition-timing-function: ease;
       -o-transition-timing-function: ease;
          transition-timing-function: ease;
  -webkit-transition-duration: .35s;
       -o-transition-duration: .35s;
          transition-duration: .35s;
  -webkit-transition-property: height, visibility;
       -o-transition-property: height, visibility;
          transition-property: height, visibility;
}