body {
    width: 80%;
    margin: auto;
}
header, footer {
    text-align: center;
}
.main_menu {
    list-style: none;
    text-align: center;
    padding: 0;
}
.main_menu li {
    padding: 10px;
}
.nav_links {
    text-align: center;
}
.prev {
    padding-right: 20px;
}
.dedication {
    text-align: right;
    margin-right: 50px;
}
.martin_img, .book_cover {
    display: block;
    margin: 20px auto;
}