hide and show elements with js using getElementById and style.display

HTML

<div class='an-element one' id='an-element'>my element 1</div>

<p>
	<button class='btn btn-primary' onclick="document.getElementById('an-element').style.display = 'block';">Show 1</button>
	<button class='btn btn-primary' onclick="document.getElementById('an-element').style.display = 'none';">Hide 1</button>
</p>

CSS

.an-element {
	height:150px;
	width:150px;
	background:#999;
	border-radius:5px;
	margin:10px;
	color:#FFF;
	text-align:center;
}