.bck{height:50px;padding-top:0;right:1rem;color:#fff;position:fixed;bottom:1rem;visibility:hidden;text-align:center;background:rgba(243,111,33,.8);width:50px;line-height:50px;transition-property:all;z-index:999}.bck.bck-on{visibility:visible}.fade{opacity:0}.bck-on.fade{opacity:1}.rightToLeft{right:-50px}.bck-on.rightToLeft{right:1rem}.bottomToTop{bottom:-50px}.bck-on.bottomToTop{bottom:1rem}.bck-leftToRight{left:-50px}.bck-on.leftToRight{left:1rem}.topToBottom{top:-50px}.bck-on.topToBottom{top:1rem}