div {
  padding: 20px;
  margin: 5px; 
  float: left;
}

#all {
  width: 93%;
  background-color: dodgerblue;
}

#caja1 {
  background-color: lightgreen;
  width: 2.6rem
}

#caja2 {
  background-color: lightblue;
  width: 2.6rem
}

#caja3 {
  background-color: tomato;
  width: 2.6rem
}