style.css

#stim1 {
	width: 15vw;
	height: 15vw;
	background: red;
}

#stim2 {
	width: 15vw;
	height: 15vw;
	background: forestgreen;
}

#stim3 {
	width: 15vw;
	height: 15vw;
	background: blue;
}


.shape {
  position:absolute;
  top:50%;
  left:50%;
  transform: translate(-50%,-50%);
}