header, h1 {
  text-align: center;
}

main img {
  display: block;
  margin: 0 auto;
}

nav a {
            text-decoration: none; 
            color: blue; 
            margin-right: 10px;
        }
        
        nav {
            text-align: center; 
            margin-bottom: 10px; 
        }