*{
    box-sizing: border-box;
}

body{
    background-color: rgb(135, 135, 143);
}
header{
    width: 90%;
    margin: 20px auto;
    font-size: 5vw;
    text-align: center;
    text-transform: capitalize;
    border-bottom: 15px double black;
}

article , footer{
    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: blue;
}
main{
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
}
img[alt="principal"], section{
    width: 90%;

}
h2{
    width: 100%;
    font-size: 2vw;
}
section > img{
    width: 50%;
    border: 1px solid black;
    margin: 10px 0px;
}
section{
    display: flex;
    flex-wrap: wrap;
    justify-content: space-between;
}

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

@media only screen and (min-width: 576px){
    img[alt="twitter"]{
    display: inline;

    }
    section{
        justify-content: center;
    }
    section > img{
        width: 33%;
        border:1px solid black;
        margin: 10px 0px;
}
}
@media only screen and (min-width: 1000px){
    img[alt="twitter"],img[alt="email"]{
    display: nowrap;

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