.grid{
    width: 300px;
    height: 300px;
    border: solid black 1px;
    display: flex;
    flex-wrap: wrap ;
}

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

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

.shooter {
    background-color: cadetblue;
    
}

.laser{
    background-color:chartreuse;
}

.boom{
    background-color:yellow;
}