title: jquery-ui draggable: change clone helper's css margin correctly
body: <p>I have a problem with setting css margin property of the cloned helper div element.</p>
  
  <p>There are three frames in the following example: green frame is the dragged items storage, blue frame is for dropping, red frame limits the place for dragging. I would like to place items in the middle of the green frame but enable the dragged item to move in the red frame close to all borders.</p>
  
  <p>So all items in the green frame have css margin: 8px auto, for the cloned helper I try to change margin to 0 with ui.helper.css('margin', '0'). The problem is that the dragged item does not want to move to the lower right corner of the red frame.</p>
  
  <p>You can find <a href="http://jsfiddle.net/0or2uauo/" rel="nofollow">jsfiddle project here</a></p>
  
  <p>HTML:</p>
  
  <pre><code>&lt;div id="main-container"&gt;
  &lt;div id="stock"&gt;
  &lt;div class="block"&gt;drag me to the right bottom corner of the red border&lt;/div&gt;
  &lt;/div&gt;
  &lt;div id="workspace"&gt;
  &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>CSS:</p>
  
  <pre><code>#main-container {
  position: absolute;
  top: 20px;
  left: 20px;
  bottom: 20px;
  right: 20px;
  border: 2px solid #ff0000;
  }
  
  #stock {
  position: absolute;
  top: 5px;
  left: 5px;
  bottom: 5px;
  width: 180px;
  border: 2px solid #00ff00;
  }
  
  #workspace {
  position: absolute;
  top: 5px;
  left: 185px;
  bottom: 5px;
  right: 5px;
  border: 2px solid #0000ff;
  }
  
  .block {
  height: 100px;
  width: 150px;
  border: 1px solid #2e6f9a;
  position: relative;
  box-shadow: 2px 2px 19px #e0e0e0;
  border-radius: 8px;
  opacity: 0.8;
  filter: alpha(opacity=80);
  background-color: white;
  text-align: center;
  font-weight: bold;
  transition: background-color 0.25s ease-in;
  
  margin: 8px auto;
  }
  </code></pre>
  
  <p>JavaScript:</p>
  
  <pre><code>$('.block').draggable({
  appendTo: '#main-container',
  containment: $('#main-container'),
  helper: 'clone',
  cursor: 'move',
  revertDuration: 100,
  revert: 'invalid',
  start: function(ev, ui) {
      ui.helper.css('margin', '0');
      ui.helper.css('background-color', 'red');
  }
  });
  
  $('#workspace').droppable({
  accept: '.block',
  tolerance: 'fit'
  });
  </code></pre>