* {
    box-sizing: border-box;
}

body {
    background-color: rgb(193, 193, 193); /* 0 - 255 */
    /*                     rojo, verde, azul*/
}

header, main {
    border: 2px solid black;
    /* medidas relativas */
    padding: 1%;
    margin: 1%;
    
    /* medidas absolutas  - no es adaptable */
    
    /* padding: 40px; 
    margin: 40px;   */
   
    border-radius: 5px;
    background-color: lightcoral;
}

section {
    background-color: greenyellow;
    margin: 2%;
    padding: 2%;
    border: 2px solid black;
    border-radius: 5px;
}

.max-50porc {
    max-width: 50%;
    max-height: 50%;
}