can i use mp4 in background css code example

Example 1: how to set background video in html

<div class="fullscreen-bg">
    <video loop muted autoplay poster="img/videoframe.jpg" class="fullscreen-bg__video">
        <source src="video/big_buck_bunny.webm" type="video/webm">
        <source src="video/big_buck_bunny.mp4" type="video/mp4">
        <source src="video/big_buck_bunny.ogv" type="video/ogg">
    </video>
</div>

Example 2: Background Video.module.css'

video.fullscreen { 
  position: fixed;
  top: 50%;
  left: 50%;
  min-width: 100%;
  min-height: 100%;
  width: auto;
  height: auto;
  z-index: -100;
  transform: translate(-50%, -50%);
}