Change background color of position aware button

$(function() {  
  $('.btn-posnawr')
    .on('mouseenter', function(e) {
            var parentOffset = $(this).offset(),
            relX = e.pageX - parentOffset.left,
            relY = e.pageY - parentOffset.top;
            $(this).find('span').css({top:relY, left:relX})
    })
    .on('mouseout', function(e) {
            var parentOffset = $(this).offset(),
            relX = e.pageX - parentOffset.left,
            relY = e.pageY - parentOffset.top;
        $(this).find('span').css({top:relY, left:relX})
    });
  $('[href=#]').click(function(){return false});
});

.btn-posnawr {
  text-align: center;
  text-decoration: none;
  line-height: 80px;
  color: #00c4ad;
  position: relative;
  display: block;
  overflow: hidden;
  width: 100%;
  height: 80px;
  max-width: 250px;
  margin: 1rem auto;
  text-transform: uppercase;
  border: 1px solid #00c4ad;
}
.btn-posnawr span {
  position: absolute;
  display: block;
  width: 0;
  height: 0;
  border-radius: 50%;
  background-color: #00c4ad;
  -webkit-transition: width 0.4s ease-in-out, height 0.4s ease-in-out;
  transition: width 0.4s ease-in-out, height 0.4s ease-in-out;
  -webkit-transform: translate(-50%, -50%);
          transform: translate(-50%, -50%);
  z-index: -1;
}
.btn-posnawr:hover {
  color: #eee;
}
.btn-posnawr:hover span {
  width: 225%;
  height: 562.5px;
}
.btn-posnawr:active {
  background-color: #00c4ad;
}

<a class="btn-posnawr" href="#">Position Aware<span></span></a>