.grid{
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  display: flex;
  flex-wrap: wrap;
  border: solid 1px;
  border-radius: 30px;
  width: 300px;
  height: 300px;
  background-color: #000;
}

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

.shooter{
  background-image: url('shuttle.png');
  background-position: center;
  background-repeat: no-repeat;
  background-size: cover;
}

.invader{
  background-image: url('cloneball.svg');
  background-position: center;
  background-repeat: no-repeat;
  background-size: cover;
  border-radius: 10px;
}

.boom{
  background-image: url('explode.png');
  background-position: center;
  background-repeat: no-repeat;
  background-size: cover;
}

.laser{
  background: linear-gradient(#ff0000, #fff);
  border-radius: 30%;
  transform: scale(0.07, 0.7);
}