Candybar button animation

HTML

<button class="button in-progress">Please wait...</button>

CSS

body {
    padding: 40px;
}

.button {
  -webkit-transition: box-shadow 0.15s  ;
  -moz-transition: box-shadow 0.15s  ;
  -ms-transition: box-shadow 0.15s  ;
  -o-transition: box-shadow 0.15s  ;
  transition: box-shadow 0.15s  ;
  border: 1px solid #b2afa5;
  border-color: #e1e0dc #c9c8c1 #b2afa5;
  text-shadow: 0 1px 0 rgba(255, 255, 255, 0.439);
  background: -webkit-linear-gradient(top, #f6f5f0, #e1e0dc);
  background: -moz-linear-gradient(top, #f6f5f0, #e1e0dc);
  background: -ms-linear-gradient(top, #f6f5f0, #e1e0dc);
  background: -o-linear-gradient(top, #f6f5f0, #e1e0dc);
  background: linear-gradient(top, #f6f5f0, #e1e0dc);
  -pie-background: linear-gradient(top, #f6f5f0, #e1e0dc);
  color: #6b635b;
  -webkit-box-shadow: rgba(255, 255, 255, 0) 0 0 1px 0, rgba(255, 255, 255, 0) 0 0 0 1px inset, white 0 1px 0 0;
  -moz-box-shadow: rgba(255, 255, 255, 0) 0 0 1px 0, rgba(255, 255, 255, 0) 0 0 0 1px inset, white 0 1px 0 0;
  -ms-box-shadow: rgba(255, 255, 255, 0) 0 0 1px 0, rgba(255, 255, 255, 0) 0 0 0 1px inset, white 0 1px 0 0;
  -o-box-shadow: rgba(255, 255, 255, 0) 0 0 1px 0, rgba(255, 255, 255, 0) 0 0 0 1px inset, white 0 1px 0 0;
  box-shadow: rgba(255, 255, 255, 0) 0 0 1px 0, rgba(255, 255, 255, 0) 0 0 0 1px inset, white 0 1px 0 0;
  display: inline-block;
  white-space: nowrap;
  margin: 0;
  cursor: pointer;
  font-size: 13px;
  line-height: normal;
  text-align: center;
  color: #6b635b;
  padding: 5px 9px;
  text-decoration: none;
  -webkit-border-radius: 3px;
  -moz-border-radius: 3px;
  -ms-border-radius: 3px;
  -o-border-radius: 3px;
  border-radius: 3px;    
}


.button.disabled {
  color: #bdbbb9;
  border: 1px solid #d3d3d3;
  cursor: auto;
  text-shadow: white 0 1px 0;
  -webkit-box-shadow: white 0 1px 0 0 inset;
  -moz-box-shadow: white 0 1px 0 0 inset;
  -ms-box-shadow: white 0 1px 0 0 inset;
  -o-box-shadow: white 0 1px 0 0 inset;
  box-shadow: white 0 1px 0 0 inset;
}


.in-progress {
      text-shadow: none;
  background:...