<div class="canvas_container left">
     <div class="canvas_wrap">
       <canvas id="original" width="150" height="150"></canvas>
       <div class="dropzone first">Drop it here!</div>
     </div>
   </div>

/** Every canvas can only get half of the screen */
   div.canvas_container {
     max-width: 50%;
     width: 50%;
   }
   /**The inner canvas container should center the other elements **/
   div.canvas_container div.canvas_wrap {
     position: relative;
     height: 100%;
     display: inline-block;
     /*vertical-align: middle; */
   }

   div.canvas_container canvas {
      display: block;
      /*position:absolute;*/
      top:0px;
      left: 0px;
   }

   /**This div should be centered**/
   div.canvas_container div.first {
     display: block;
     margin: auto;
     position: absolute;
     top: 0; left: 0; bottom: 0; right: 0;
   }