Very simple CSS rotation.


.dropdown-container a.dropdown-button span::after {
-webkit-transition-duration: 0.5s;
-moz-transition-duration: 0.5s;
-o-transition-duration: 0.5s;
transition-duration: 0.5s;
-webkit-transition-property: -webkit-transform;
-moz-transition-property: -moz-transform;
-o-transition-property: -o-transform;
transition-property: transform; }

.dropdown-container.active a.dropdown-button span::after {
-webkit-transform: rotate(46deg);
-moz-transform: rotate(46deg);
-o-transform: rotate(46deg);
-ms-transform: rotate(46deg);
transform: rotate(46deg);
}