body {
    display: flex;
    justify-content: center;
    background-image: radial-gradient(navy, black);
	background-image: moz-radial-gradient(navy, black);
}
button {
	background-color:gray;
	color:black;
	font-size:20;
    padding:20px;
    border-radius:25%;
}
#center {
    position: absolute;
    top: 50%;
}
button:hover {
	background-color:maroon;
}