#canvas{
  position: relative;
  width: 40vmin;
  height: 40vmin;
  background-color: white;
  margin: 0 auto;
}
#col1{
  left: vmin;
  position: absolute;
  background-color:blue;
  width: 15vmin;
  height: 15vmin;
}
#col2{
  left: 15vmin;
  position: absolute;
  background-color: red;
  width: 15vmin;
  height: 15vmin;

}
#col3{
  top:0;
  left:30vmin;
  position: absolute;
  background-color: yellow;
  width: 15vmin;
  height: 15vmin;
}