*{
    box-sizing: border-box;
}

body{
    background-color: peru;
}

header{
    width: 90%;
    margin: 20px auto;
    font-size: 7vw;
    text-align: center;
    text-transform: capitalize;
    color: green;
    border-bottom: 15px double black;
}

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

}

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

li{
    list-style-type: none;
    width: 25%;
    font-size: 1.2vw;
    padding: 1px 10px;
    border-right: 1px solid black;
}

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

li > img{
    margin: 0px 10px;
}

span{
    color: cyan;
}

@media screen and (min-width: 576px){
    img[alt="stu"], img[alt="twi"] {
        display: inline;
    }
}

footer{
    width: 90%;
    margin: 20px auto;
    font-size: 3vw;
    text-align: center;
    color: red;
}

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

img[alt="principal"], section{
    width: 60%;
}

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

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

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

img[alt ="stu" ], img[alt="twi"], 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 black;
        margin: 10px 0px;
    }

}

@media screen and (min-width: 1000px){
    img[alt="twi"], img[alt="mail"]{
        display: inline;
    }
    main{
        flex-wrap: nowrap;
    }
    img[alt="principal"], section{
        width: 75%;
    }
    section{
        width: 28%;
    }
    main > section > img{
        width: 48%;
    }

}