* {
    box-sizing: border-box;
}

html {
    font-family: "Lucida Sans", sans-serif;
}

body {
    margin: 0;
}

/* CONTENEDOR PRINCIPAL */

.contenedor {
    width: 70%;
    margin: 60px auto;
    border: 3px solid red;
    padding: 5px;
}

/* FILA */

.row::after {
    content: "";
    clear: both;
    display: block;
}

/* COLUMNAS */

[class*="col-"] {
    float: left;
    padding: 25px;
    border: 1px solid black;
}

/* ANCHO DE COLUMNAS */

.col-1 { width: 8.33%; }
.col-2 { width: 16.66%; }
.col-3 { width: 25%; }
.col-4 { width: 33.33%; }
.col-5 { width: 41.66%; }
.col-6 { width: 50%; }
.col-7 { width: 58.33%; }
.col-8 { width: 66.66%; }
.col-9 { width: 75%; }
.col-10 { width: 83.33%; }
.col-11 { width: 91.66%; }
.col-12 { width: 100%; }


/* ========================= */
/* TABLETS */
/* ========================= */

@media (max-width: 900px) {

    .contenedor {
        width: 90%;
        margin: 40px auto;
    }

    [class*="col-"] {
        padding: 20px;
    }

}


/* ========================= */
/* CELULARES */
/* ========================= */

@media (max-width: 600px) {

    .contenedor {
        width: 95%;
        margin: 20px auto;
        padding: 3px;
    }

    [class*="col-"] {
        width: 100%;
        float: none;
        padding: 15px;
    }

}