Bootstrap 4 responsive embeds CSS

responsive-embeds.css

/* Compiled CSS from Bootstrap 4's responsive embeds */
.embed-responsive {
    position: relative;
    display: block;
    width: 100%;
    padding: 0;
    overflow: hidden
}
.embed-responsive::before {
    display: block;
    content: ""
}
.embed-responsive .embed-responsive-item,.embed-responsive iframe,.embed-responsive embed,.embed-responsive object,.embed-responsive video {
    position: absolute;
    top: 0;
    bottom: 0;
    left: 0;
    width: 100%;
    height: 100%;
    border: 0
}
.embed-responsive-21by9::before {
    padding-top: 42.85714%
}
.embed-responsive-16by9::before {
    padding-top: 56.25%
}
.embed-responsive-4by3::before {
    padding-top: 75%
}
.embed-responsive-1by1::before {
    padding-top: 100%
}

/**
* HTML Usage: 
* <div class="embed-responsive embed-responsive-16by9">
*   <iframe class="embed-responsive-item" src="..."></iframe>
* </div>
**/