CSS: Responsive vídeos YouTube

<div class="video-container">
<iframe >...</iframe>
</div>

<style>
.video-container {
position:relative;
padding-bottom:56.25%;
padding-top:30px;
height:0;
overflow:hidden;
}

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