[Wordpress] Responsive embed videos without plugins

function.php

<?php

/*  Add responsive container to embeds
/* ------------------------------------ */ 
function id_embed_html( $html ) {
    return '<div class="video-container">' . $html . '</div>';
}
 
add_filter( 'embed_oembed_html', 'id_embed_html', 10, 3 );
add_filter( 'video_embed_html', 'id_embed_html' ); // Jetpack

style.css

.video-container {
  position: relative;
  padding-bottom: 56.25%;
  height: 0;
  overflow: hidden;
}

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