@mixin cwui-backtotop {
  .backtotop {
    background: url("#{$www-assets}/images/backtotop-button.png") 0 0 no-repeat;
    background-image: url("#{$www-assets}/images/backtotop-button.svg"),
      linear-gradient(transparent, transparent);
    bottom: rem-calc(20);
    height: rem-calc(40);
    opacity: .65;
    position: fixed;
    right: rem-calc(20);
    transition: 100ms opacity ease-in,
                100ms transform cubic-bezier(.8, .5, .2, 1.4),
                250ms bottom ease-in-out;
    width: rem-calc(40);
    z-index: 999;
  
    &:hover {
      opacity: .85;
    }
  
    &.backtotop--hidden {
      bottom: -50vh;
    }
  
    a {
      display: block;
      height: 100%;
    }
  }
}