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

/*etiquetas*/

header {
    background: #72ee25;
    width: 100%;
    height: 8rem;
}

main{
    display: flex;
    justify-content: flex-start;
}

section {
    background: #25aeee;
    width: 100%;
    display: flex;
    justify-content: flex-start;
    flex-direction: column;
}

section div article {
    background: #ef9c25;
    width: 33%;
    height: 15rem;
    margin: 0.5em;
}

section div {
    width: 100%;
    display: flex;
    justify-content: space-around;
}

aside {
    background: #ccc;
    width: 100;
    display: flex;
    justify-content: center;    
 }

footer {
    background: #72ee25;
    width: 100%;
    height: 8rem;
}


/*clases*/

.contenedor{
    max-width: 65rem; margin: auto;
}

.ancho75 {
    width: 70%;
}

.ancho25 {
    width: 30%;    
}