.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;
}