CSS
 .videoWrapper {
        position: relative;
        padding-bottom: 56.25%; /* 16:9 56.25% */
        padding-top: 0px;
        height: 0;
    }
    .videoWrapper iframe {
        position: absolute;
        top: 0;
        left: 0;
        width: 80%;
        height: 80%;
    }

<div class="videoWrapper">
<iframe width="560" height="315" src="https://www.youtube.com/embed/EFROb5nEcQM?rel=0&showinfo=0" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen></iframe></div>