Bulma class: .hero-video

<section class="hero is-fullheight video">
    <div class="hero-video">
        <video poster="img/poster.jpg" playsinline autoplay muted loop>
            <source src="video.webm" type="video/webm">
        </video>
    </div>
    <div class="hero-body">
        <div class="container">
            ...
        </div>
    </div>
    <div class="hero-foot">
        <div class="has-text-centered">
            ...
        </div>
    </div>
</section>

Preview

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