/*CSS*/
.youtube .play-button {
	width: 90px;
	height: 60px;
	background-color: #333;
	box-shadow: 0 0 30px rgba( 0,0,0,0.6 );
	z-index: 1;
	opacity: 0.8;
	border-radius: 6px;
}
.youtube .play-button:before {
	content: "";
	border-style: solid;
	border-width: 15px 0 15px 26.0px;
	border-color: transparent transparent transparent #fff;
}

.youtube img,
.youtube .play-button {
	cursor: pointer;
}
.youtube img,
.youtube iframe,
.youtube .play-button,
.youtube .play-button:before {
	position: absolute;
}
.youtube .play-button,
.youtube .play-button:before {
	top: 50%;
	left: 50%;
	transform: translate3d( -50%, -50%, 0 );
}

.youtube img {
	width: 100%;
}

.youtube iframe {
	height: 100%;
	width: 100%;
	top: 0;
	left: 0;
}
/*CSS*/

/*JS*/
(function() {

	var youtube = document.querySelectorAll(".youtube");

	for (var i = 0; i < youtube.length; i++) {

		var source = "https://img.youtube.com/vi/" + youtube[i].dataset.embed + "/sddefault.jpg";

		var image = new Image();
		image.src = source;
		image.addEventListener("load", function() {
			youtube[i].appendChild(image);
		}(i));

		youtube[i].addEventListener("click", function() {

			var iframe = document.createElement("iframe");

			iframe.setAttribute("frameborder", "0");
			iframe.setAttribute("allowfullscreen", "");
			iframe.setAttribute("src", "https://www.youtube.com/embed/" + this.dataset.embed + "?rel=0&showinfo=0&autoplay=0");

			this.innerHTML = "";
			this.appendChild(iframe);
		});
	};

})();
/*JS*/

/*HTML*/
<div data-embed="YOUTUBE_VIDEO_ID" class="video-modal youtube">
  <div class="play-button"></div>
</div>
/*HTML*/