*{
    box-sizing: border-box;
}

body{
   /* background-color: aquamarine; */
}

header{
    width: 90%;
    margin: 20px auto;
    font-size: 7vw;
    color: grey;
    border-bottom: 7px double black;
}

article, footer,main{
    width: 90%;
    margin: 20px auto;
}

footer{
    color: grey;
}

ul{
    display: flex;
    flex-wrap: nowrap;
}

li{
    list-style-type: none;
    width: 22%;
    font-size: 1.2vw;
    padding: 1px 20px;
    border-right: 3px solid rgb(36, 33, 33);
}

li:last-of-type{
    border: none;
}

li > img{
    margin: 0px 1px;
}

span{
    color: blue;
}

main{
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
}

img[alt="principal"], section{ /* Para seleccionar una imagen en específico */
    width: 90%;
}

h2{
    font-size: 2vw;
    width: 100%;
}

section{
    display: flex;
    flex-wrap: wrap;
    justify-content: space-between;
}

section > img {
    width: 50%;
    border: 1px solid grey;
    margin: 10px 0px;
}

img[alt="stu"], img[alt="twitter"], img[alt="mail"]{
    display: none;
}

@media screen and (min-width: 576px){

    img[alt="stu"]{
        display: inline;
    }

    section{
        justify-content: center;
    }

    section > img {
        width: 33%;
        border: 1px solid grey;
        margin: 10px 0px;
    }

    img[alt="twitter"], img[alt="mail"]{
    display: none;
}

}

@media screen and (min-width: 993px){

    img[alt="twitter"], img[alt="mail"]{
        display: inline;
    }

}

@media screen and (min-width: 1000px){
    
    img[alt="twitter"], img[alt="mail"]{
        display: inline;
    }

    main{
        flex-wrap: nowrap;
        justify-content: space-between;
    }

    img[alt="principal"]{
        width: 150%;
    }

    section > img {
        width: 50%;
        border: 1px solid grey;
        margin: 10px 0px;
    }

}