result-embed-responsively.html

<style>
    .embed-container {
        position: relative;
        padding-bottom: 56.25%;
        padding-top: 30px;
        height: 0;
        overflow: hidden;
        max-width: 100%;
        height: auto;
    }
    .embed-container iframe, .embed-container object, .embed-container embed {
        position: absolute;
        top: 0;
        left: 0;
        width: 100%;
        height: 100%;
    }
</style>
<div class='embed-container'>
    <iframe src='http://www.youtube.com/embed/jKQz6A8Mi3E' frameborder='0' allowfullscreen></iframe>
</div>

http://www.romitello.com/2019/02/high2-2.html