* { box-sizing: border-box; }
body {
    font-family: Arial, Helvetica, sans-serif;
}
#wrapper {
    width: 80%;
    margin-left: auto;
    margin-right: auto;
    border: think solid black;
}
header {
    margin: 10px;
    padding: 10px;
    background-color: midnightblue;
    color: white;
}
nav {
    display: flex;
    justify-content: center;
}
nav > div {
    background-color:midnightblue;
    color:aliceblue;
    margin: 10px;
    padding: 10px;
    font-size: 20px;
    text-align: center;
    flex: 1;
}
main {
    display: flex;
}
main > div {
    background-color:midnightblue;
    color:aliceblue;
    margin: 10px;
    padding: 10px;
}
.left {
    flex: 2;
}
.right {
    flex: 1;
}
footer {
    background-color: midnightblue;
    margin: 10px;
    padding: 10px;
}
footer > p {
    text-align: center;
    color: white;
}
@media only screen and (max-width: 1024px) {
    #wrapper {
        width: 100%;
        border: none;
    }
}
@media only screen and (max-width: 510px) {

    nav {
        flex-direction: column;
    }  
    nav > div {
        text-align: center;
        width: auto;
        margin: 5px;
    } 
    main {
        flex-direction: column;
    }  
    main > div {
        margin: 5px;
    }
}