title: How to grey out a box in CSS
body: <p>I have an element #messages-box, which include title, body, sender, avatar and excerpt. Now, I would like to grey out all elements in #message-box.</p>
  
  <p>I know I can set properties of each of elements to make them all grey. But is there a way so that I can just change properties of #message-box? </p>
  
  <p>All I need is something like a grey veil covers #message-box.</p>
  
  <p>Thank you.</p>