checkbox-checked.scss

&:checked
{
    & + label
    {
        &:before{
          border-color: $theme;
          background-color: $theme;
        }

        &:after{
          width: 6px;
          height: 13px;
          top: 3px;
          left: 5px;

          color: #fff;
          border-top: 2px solid transparent;
          border-left: 2px solid transparent;
          border-right: 2px solid #fff;
          border-bottom: 2px solid #fff;

          -webkit-transform: rotate(37deg);
              -ms-transform: rotate(37deg);
               -o-transform: rotate(37deg);
                  transform: rotate(37deg);
        }
    }
}