style.css

.button{
	width:400px; /*same as the height*/
	height:400px; /*same as the width*/
	display: block;
	/*
	background-color:#ff0000;
	*/
	background-color: #58aa00;
	border:1px solid #58aa00; /*same colour as the background*/
	color:#fff;

	font-size:500%;
	text-align: center;
	text-shadow: 2px 2px #555;

	/*set the border-radius at half the size of the width and height*/
	-webkit-border-radius: 50%;
	-moz-border-radius: 50%;
	border-radius: 50%;
	/*give the button a small drop shadow*/
	-webkit-box-shadow: 0 0 10px rgba(0,0,0, .75);
	-moz-box-shadow: 0 0 10px rgba(0,0,0, .75);
	box-shadow: 2px 2px 15px rgba(0,0,0, .75);
}
.button:hover{
	background:#490;
	border:1px solid #490;
	/*reduce the size of the shadow to give a pushed effect*/
	-webkit-box-shadow: 0px 0px 5px rgba(0,0,0, .75);
	-moz-box-shadow: 0px 0px 5px rgba(0,0,0, .75);
	box-shadow: 0px 0px 5px rgba(0,0,0, .75);
}