Изменение свойст элемента

<div id="work2"><link rel="stylesheet" href="//code.jquery.com/ui/1.12.1/themes/base/jquery-ui.css">
  <script src="https://code.jquery.com/jquery-1.12.4.js"></script>
  <script src="https://code.jquery.com/ui/1.12.1/jquery-ui.js"></script>
<div class="work2.1">
<form action="#">
  <div id="circle" style="width: 250px; height: 250px; background: yellow;"></div>
  <fieldset>
    <label for="radius-button">Circle radius</label>
    <select name="radius" id="radius" style="display: none;">
      <option value="50">50px</option>
      <option value="100">100px</option>
      <option value="150" selected="selected">150px</option>
      <option value="200">200px</option>
      <option value="250">250px</option>
    </select>
    <label for="color-button">Circle color</label>
    <select name="color" id="color" style="display: none;">
      <option value="black">Black</option>
      <option value="red">Red</option>
      <option value="yellow" selected="selected">Yellow</option>
      <option value="blue">Blue</option>
      <option value="green">Green</option>
    </select>
  </fieldset>
</form>
</div>
</div>

Results: