.caja1{background-color: red;
width:100px;
height:50px;
float:left
}
.caja2{background-color:green;
float:left;
width:150px;
height:50px;
}
.caja3{background-color:blue;
width:60%;
height:100px;
float:left
}
.caja4{background-color:grey;
width:30%;
height:150px;
float:left
}