Image inside a button only shown in half in emulator

ionic-v1
#1

It’s working fine in browser. But in my emulator (also in device. The top button should be in full circle actually):

image
屏幕快照 2016-01-30 上午11.48.20.png728×414 259 KB

My html:

<div class="float-bottom">
  <button class="button button-clear button-block" ng-click="camera()">
    <img class="bottom-button" src="img/camera-button.png" alt="">
  </button>
  <div class="spacer" style="height: 10px;"></div>
  <button class="button button-clear button-block" ng-click="gallery()">
     <img class="bottom-button" src="img/gallery-button.png" alt="">
  </button>
</div>

Css:

.float-bottom {
  position: absolute;
  bottom: 0px; width: 100%;
  z-index: 2147483647;
}

img.bottom-button {
   width:200px;
   height: auto;
}

Any idea?