title: What do /deep/ and ::shadow mean in a CSS selector?
body: <p>In looking at Polymer, I see the following CSS selector in the <em>Styles</em> tab of Chrome 37's developer tools:</p>
  
  <p><img src="https://i.stack.imgur.com/L87ZX.png" alt="enter image description here"></p>
  
  <p>I've also seen a selector with pseudo selector <code>::shadow</code>.</p>
  
  <p>So, what do <code>/deep/</code> and <code>::shadow</code> in a CSS selector mean?</p>