*{
    box-sizing: border-box;
    margin: 0;
    padding: 0 !important;
}

body{
    background-color: pink;
}

.caja1{
    background-color: yellow;
    border: 2px solid #000000;
    
}

.caja2{
    background-color: brown;
    border: 2px solid #000000;
}