body{margin:0;font-family:Arial,sans-serif}header{position:fixed;width:100%;background:#333;color:#fff;padding:10px 0}header nav ul{list-style:none;display:flex;justify-content:center;margin:0;padding:0}header nav ul li{margin:0 15px}header nav ul li a{color:#fff;text-decoration:none}section{padding-top:60px}