body, html {
    height: 100%;
    margin: 0;
	background-color: #121212;
	color: #ffffff;
}

.center-screen {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;             /* viewport height */
}

game {
    display: block;
    margin-left: auto;
    margin-right: auto;
    background-color: lightgray;
}