title: html2canvas z-index not effect
body: <p>I am using html2canvas library for converting a div to png. </p>
  
  <p>I have an issue about <code>z-index</code>. As you can see on image, I have boxes. Inside a box I have a div for background coloring (<code>z-index: 0</code>), its growing with height value and a div for number (<code>z-index: 1</code>). It works fine on browser as usual but when I try to take image, it seems like <code>z-index</code> doesn't work.</p>
  
  <p>normal on browser:
  <a href="https://i.stack.imgur.com/q4MGf.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/q4MGf.png" alt="enter image description here"></a></p>
  
  <p>issue on image version:
  <a href="https://i.stack.imgur.com/IVBt4.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/IVBt4.png" alt="enter image description here"></a></p>
  
  <p>Any help, I will be grateful.</p>