.header-video-wrapper {
    position: relative;
    width: 100%;
    height: 500px;
    overflow: hidden;
}
.header-video {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    object-fit: cover;
}
@media (max-width: 768px) {
    .header-video-wrapper {
        height: 420px;      /* change to adapt */
    }
}