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