I'm trying to position a button to center of screen. But it looks like there's an offset of 20px to the button.It appears 20px vertically away from the exact center.
Here's how it looks:
Here's the html body:
<body ng-app="starter" class="platform-ios platform-cordova platform-webview">
    <ion-pane>
      <ion-content>
          <div  id="cool-button-div">
          <button class="button button-block button-calm">Cool!</button>
          </div>
      </ion-content>
    </ion-pane>
  </body>
and CSS:
  #cool-button-div {
    position: relative;
    width:200px;
    margin:auto;
    margin-top:50%;
}
I can position the button by calculating the exact center of screen and if I use top : 250px, it works but if I use top:50% it doesnt work.
Note: I do not want to use additional divs which act like spacer views.

 
    