header, main, footer {
    margin: 0 aut;
    width: 1000px;
}
nav ul {
    padding: 0;
    list-style-type: none;
    display: flex;
    justify-content: space-between;
}
nav a {
    text-decoration: none;
    border-color: #12E21A;	
}
nav a:hover {
    background-color: #CEE20B;
    color: #12EFDB;	
}