Cabecera: header

                h1 {color: purple;}             <-- 0 0 0 1   (1) --> 
                h1 {color: grey;}               <-- 0 0 0 1   (1) --> 
                #caja .cabecera h1 {color: red} <-- 0 1 1 1 (111) --> MAYOR PRIORIDAD
                #caja header h1 {color: blue;}  <-- 0 1 0 2 (102) -->         
                header h1 {color: lime;}        <-- 0 0 0 2   (2) -->