* { box-sizing: border-box;}
body {
    font-family: Arial, Helvetica, sans-serif;
}
#wrapper {
    width: 80%;
    margin-left: auto;
    margin-right: auto;
    border: thin solid black;
}
header {
    margin: 10px;
    padding: 10px;
    background-color: grey;
    color: white;
}
header > img {
    width: 20%;
    height: auto;
    float: right;
}
.clearright {
    clear: right;
}
nav {
    display: flex;
    justify-content: center;
    text-align: center;
    flex: 1;
}
nav > div {
    background-color: #f1f1f1;
    margin: 10px;
    padding: 10px 20px;
    font-size: 20px;
}
nav > div > a {
    color: steelblue;
    font-weight: bold;
    text-decoration: none;
}
nav > div > a:hover {
    color: royalblue;
    text-decoration: underline;
}
main {
    display: flex;
}
main > div {
    background-color: #f1f1f1;
    margin: 10px;
    padding: 10px;
    width: 100%;
}
table {
  font-family: arial, sans-serif;
  border-collapse: collapse;
  width: 90%;
  margin-left: auto;
  margin-right: auto;
}

td, th {
  border: 1px solid #dddddd;
  text-align: left;
  padding: 8px;
}

tr:nth-child(even) {
  background-color: whitesmoke;
}
label { 
    float: left; 
    display: block; 
    text-align: right; 
    width: 10em; 
    padding-right: 1em; 
}
input, textarea { 
    display: block; 
    margin-bottom: 2em; 
}
input[type="submit"] { 
    margin-left: 12em; 
}
form { 
    padding: 3em; 
}
footer {
    background-color: gainsboro;
    margin: 10px;
    padding: 10px;
}
footer p {
    text-align: center;
}
@media only screen and (max-width: 900px) {
    #wrapper {
        width: 100%;
        border: none    ;
    }
    header > img {
        width: 25%;
        height: auto;
        float: right;
    }
}
@media only screen and (max-width: 510px) {

    nav {
        flex-direction: column;
    }   
    main {
        flex-direction: column;
    }   
    nav > div {
        width: auto;
        margin: 5px;
    }
    main > div {
        margin: 5px;
    }
    header > img {
        width: 40%;
        height: auto;
        float: right;
    }
}