body {
  background-color: aliceblue;
  margin: 0px;  
}

button{  
  position: fixed;
  top: 1em;
  left: 1em;
  z-index: 2;    
}


#pixel {
}

#rouge {
  position: absolute;  
  height: 100vh;
  width: 33.3vw;
}
#vert {
  position: absolute;  
  left: 33.3vw;
  height: 100vh;
  width: 33.3vw;
}
#bleu {
  position: absolute;  
  left: 66.6vw;
  height: 100vh;
  width: 33.3vw;
}