*{
margin: 0;
padding:0;
text-align: center;
}

body {
    background-color: #000000;
    width: 100vw;
    height: 100dvh;
}
    div {
        width: 100%;
        position: relative;
        top: 50%;
        left: 50%;
        transform: translate(-50%, -50%);
    }
video {
    max-width: 100%;
    max-height: 100%;
    object-fit: cover;
}

@media screen and (min-width: 768px){
    video {
        width: 80%;
    }
}
@media screen and (max-width: 767px){
    video {
        width: 100%;
    }
}