CSS background cut
<p>this is my code, and as you can see <em>body</em> has some background image, and <em>#cont</em> should be white. But I want my <em>div</em> elements to be transparent in a way that I can see body background image. Any CSS tricks that can do that?</p>

<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-css lang-css prettyprint-override"><code>body {
  margin: 0;
  border: 0;
  padding: 0;
  height: 100%;
  width: 100%;
  background-image: url(image.png);
  background-position: center;
  background-repeat: no-repeat;
  background-size: cover;
}
#cont {
  margin: 0;
  border: 0;
  padding: 0;
  background-color: white;
}
#cont div {
  margin: 20px;
  border: 1px solid gray;
  padding: 0;
  width: 50px;
  height: 50px;
  float: left;
}</code></pre>
<pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;div id="cont"&gt;
  &lt;div&gt;&lt;/div&gt;
  &lt;div&gt;&lt;/div&gt;
  &lt;div&gt;&lt;/div&gt;
  &lt;div&gt;&lt;/div&gt;
  &lt;div&gt;&lt;/div&gt;
  &lt;div&gt;&lt;/div&gt;
&lt;/div&gt;</code></pre>
</div>
</div>
</p>