<style>

.videoWrapper {
    position: relative;
    padding-bottom: 56.25%; /* 16:9 */
    padding-top: 25px;
    height: 0;
    border: 1px solid #c8d4f3;
}
.videoWrapper iframe {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
}

</style>

<div class="videoWrapper">
  <iframe width="100%" src="" frameborder="0" gesture="media" allow="encrypted-media" allowfullscreen></iframe>
</div>