DEMO: https://codepen.io/developit/pen/ZXqGKE

beautiful-html5-dialog.css

dialog {
	position: fixed;
	top: 50%;
	left: 50%;
	right: auto;
	padding: 30px;
	transform: perspective(500px) translate(-50%, -50%);
	background: linear-gradient(to bottom, #FFF, #F4F4F4) #FFF;
	border: none;
	border-radius: 3px;
	box-shadow: 0 10px 40px rgba(0, 0, 0, 0.3);
	text-align: center;
	transform-origin: 50% 50%;
	animation: dialog 300ms cubic-bezier(.3,0,.1,1.4) forwards 1;
	will-change: transform, opacity;
}

@keyframes dialog {
	from {
		transform: perspective(500px) translate(-50%, -25%) rotateX(45deg) scale(0.1);
		opacity: 0;
	}
}

dialog::backdrop {
	opacity: 0;
	will-change: opacity;
	cursor: no-drop;

	/** option 1: "grey" */
	/*
  background: rgba(0,0,0,0.3);
  */

	/** option 2: "checkerboard" */
  /*
	background: url('data:image/svg+xml;utf8,<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 2 2"><rect x="0" y="0" width="1" height="1" fill="rgba(255,255,255,0.2)" /><rect x="1" y="1" width="1" height="1" fill="rgba(255,255,255,0.2)" /></svg>') rgba(0,0,0,0.3);
	background-size: 2px 2px;
	*/
	
	/** option 3: "zoom" */
	background: radial-gradient(circle at center, rgba(50,50,50,0.5), rgba(0,0,0,0.5));
	animation: backdrop 500ms ease forwards 1;
}

@keyframes backdrop {
	from { opacity: 0; }
	to { opacity: 1; }
}

demo.html

<link type="stylesheet" href="beautiful-html5-dialog.css">

<button onClick="dialog.showModal()">Open Dialog</button>

<dialog id="dialog">
	<p>This is the dialog content.</p>
	<button onClick="dialog.close()">Close</button>
</dialog>