Question: I want to know which is a good way to use a video as a background, like is used for example in Square Cash: <https://square.com/cash>

Answer: 
```
<div id="video-container">
<video autoplay loop poster="http://media.w3.org/2010/05/sintel/poster.png" muted="muted">
                    <source id="mp4" src="http://media.w3.org/2010/05/sintel/trailer.mp4" type="video/mp4">
                    <source id="webm" src="http://media.w3.org/2010/05/sintel/trailer.webm" type="video/webm">
                    <source id="ogv" src="http://media.w3.org/2010/05/sintel/trailer.ogv" type="video/ogg">
                    Your browser does not support the video tag. I suggest you upgrade your browser.
                </video>
</div><!-- end video-container -->

#video-container {
    top:0%;
    left:0%;
    height:100%;
    width:100%;
    overflow: hidden;
        position: absolute;
}
video {
    position:absolute;
    z-index:0;
        width: 100%;
}

```
Added `object-fit: cover;` for video to act like `background-size: cover;`

```css
* {
  box-sizing: border-box;
}

body {
  margin: 0;
  padding: 0;
}

.videobg {
  height: 100vh;
  overflow: hidden;
  padding: 5vh;
  position: relative; /* requires for to position video properly */
}

video {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  z-index: -1;
  object-fit: cover; /* combined with 'absolute', works like background-size, but for DOM elements */
}
```

```html
<div class="videobg">
  <video playsinline webkit-playsinline autoplay loop muted>
  <source src="http://techslides.com/demos/sample-videos/small.mp4" type="video/mp4">
</video>
  <img src="https://dummyimage.com/200x200/cc0000/ccc.jpg">
</div>
```