Button on top of Background Image?

This is the Code I have in HTML. I want to add a button over the Image

<link rel="stylesheet" href="css/style.css">
<div id="bg">
<img src="img/bg.png" alt="">

</div>
<img src="img/Vote1.png" height="250" width="500">

CSS:

#bg {
  position: fixed; 
  top: -50%; 
  left: -50%; 
  width: 200%; 
  height: 200%;
}
#bg img {
  position: absolute; 
  top: 0; 
  left: 0; 
  right: 0; 
  bottom: 0; 
  margin: auto; 
  min-width: 50%;
  min-height: 50%;
}