.center {
    text-align: center;
    margin: auto;
}

ul {
    list-style-type: none;
    margin: 0;
    padding: 0;
    overflow: hidden;
    background-color: #dddddd;
}

li {
    float: left;
    color: green;
}

li a {
    display: block;
    padding: 8px;
    color: blue;
}

a {
    padding: 0px 25px 0px 25px;
}

img {
    max-width: 100%;
    height: auto;
}