a {
    color: blue;
}

a:hover {
    color: red;
}

form nav {
    text-align: center;
}

.odd {
    background-color: gainsboro;
}

header h1 {
    text-align: center;
}

header nav {
    border: 1px solid gray;
    margin: 0.5em;
    padding: 0.5em;
    text-align: center;
}