<canvas style="width:{{width}}; height: {{height}};" canvas-id="firstCanvas">
  <cover-view class="button_full" bindtap="saveIMG" style="position: fixed; height:50px; padding:0px; line-height:50px; text-align:center; bottom:0px; color:-sharpFFF;"></cover-view>
</canvas>

the page layout is as above, which is normal when the Android virtual button is displayed, but after putting it away, the layout of the Save Picture button has changed. what is the problem?