Need to add below code to implement :
css*****************
.video-block {
position: fixed;
top: 50%;
left: 50%;
z-index: 1;
min-width: 100%;
min-height: 100%;
width: auto;
height: auto;
transform: translate(-50%, -50%);
}
.text-wrapper {
position: relative;
top: 30%;
z-index: 2;
margin: 0px auto;
max-width: 720px;
text-align: center;
}
html code ************
<body>
<div class="text-wrapper">
<h1>Heading</h1>
<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Suscipit qui voluptatum enim est deserunt assumenda, aspernatur quam aperiam!</p>
<a href="#" class="content__cta">Link</a>
</div>
<video id="demo" class="video-block" autoplay="autoplay" loop="loop" muted="" width="300" height="150">
<source src="http://thenewcode.com/assets/videos/polina.webm" type="video/webm">
<source src="http://thenewcode.com/assets/videos/polina.mp4" type="video/mp4">
<source src="media/demo.ogv" type="video/ogg" />
</body>
I Hope this will help you to implement -:)