Responsive YouTube embeds

From https://themeskills.com/make-embedded-youtube-videos-responsive-wordpress/

Get the iframe embed code, and paste it within the following div.

<div class="youtube-responsive-container"><iframe ...></iframe></div>

add the following CSS to the site:

.youtube-responsive-container {
position:relative;
padding-bottom:56.25%;
padding-top:30px;
height:0;
overflow:hidden;
}

.youtube-responsive-container iframe, .youtube-responsive-container object, .youtube-responsive-container embed {
position:absolute;
top:0;
left:0;
width:100%;
height:100%;
}