<div>当a <input>或者<a>:focus'd(或任何其他动态伪类？)时,如何更改父级的背景？
例如
<div id="formspace">
<form>
<label for="question">
How do I select #formspace for the case when a child is active?</label>
<input type="text" id="question" name="answer"/></form></div>