Add wrapper div to oEmbed WordPress objects

functions.php

// https://gist.github.com/jlengstorf/ce2470df87fd9a892f68

function setup_theme(  ) {
    // Theme setup code...
    
    // Filters the oEmbed process to run the responsive_embed() function
    add_filter('embed_oembed_html', 'responsive_embed', 10, 3);
}
add_action('after_setup_theme', 'setup_theme');
/**
 * Adds a responsive embed wrapper around oEmbed content
 * @param  string $html The oEmbed markup
 * @param  string $url  The URL being embedded
 * @param  array  $attr An array of attributes
 * @return string       Updated embed markup
 */
function responsive_embed($html, $url, $attr) {
    return $html!=='' ? '<div class="embed-container">'.$html.'</div>' : '';
}

style.less

.embed-container {
    position: relative;
    padding-bottom: 56.25%;
    padding-top: 30px;
    height: 0;
    overflow: hidden;
    max-width: 100%;
    height: auto;

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