title: particles.js not covering entire page
body: <p>I'm trying to use <a href="http://vincentgarreau.com/particles.js/" rel="noreferrer">particles.js </a>as background, but I am not able to set the canvas as a full-size background.</p>
  
  <p>I tried at least 10 different solution from similar issues but nothing worked.
  The canvas always results as as an element having width-height ratio as the screen but it doesn't cover it as a whole when it is resized.
  In addiction, it won't set as background but as a child of the body, over or below the remaining elements.</p>
  
  <p>I simplified the code as much as possible and the problem still persist. </p>
  
  <p><a href="https://i.stack.imgur.com/k1xO1.png" rel="noreferrer">Example of the problem</a></p>
  
  <p>HTML</p>
  
  <pre><code>&lt;!DOCTYPE HTML&gt;
  
  &lt;html&gt;
      &lt;head&gt;
          &lt;title&gt;Try&lt;/title&gt;
          &lt;meta charset="utf-8" /&gt;
          &lt;meta name="viewport" content="width=device-width, initial-scale=1.0, minimum-scale=1.0, maximum-scale=1.0, user-scalable=no"&gt;
          &lt;link rel="stylesheet" media="screen" href="css/style.css"&gt;
      &lt;/head&gt;
  
      &lt;body&gt;
          &lt;div id="particles-js"&gt;&lt;/div&gt;
          &lt;div&gt;
              &lt;p&gt;Something here&lt;/p&gt;
          &lt;/div&gt;
      &lt;/body&gt;
  
      &lt;script src="assets/js/particles.js"&gt;&lt;/script&gt;
      &lt;script src="assets/js/app.js"&gt;&lt;/script&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>CSS</p>
  
  <pre><code>canvas{
    display:block;
    vertical-align:bottom;
    position: absolute;
  }
  
  /* ---- particles.js container ---- */
  
  #particles-js{
    position: absolute;
    width: 100%;
    height: 100%;
    background-color: #b61924;
    background-image: url('');
    background-size: cover;
    background-position: 50% 50%;
    background-repeat: no-repeat;
    top: 0;
  }
  </code></pre>
  
  <p>APP.JS and PARTICLES.JS can be downloaded from the owner's website posted before.
  I'm using themas they are at the moment</p>
  
  <p>Thanks for any help</p>