html{
    background-image: url(images/html-greyscale-background.jpg);
}
body{
    margin: 0%;
    display: grid;
     place-items: center;
}
.grid {
	width: 300px;
	height: 300px;
	border: solid black 1px;
	display: flex;
	flex-wrap: wrap;
}

.grid div {
	width: 20px;
	height: 20px;
}

.invader {
	background-color: purple;
	border-radius: 10px;
}

.shooter {
	background-color: green;
}

.laser {
	background-color: orange;
}

.boom {
	background-color: red;
}