headerAuthor.php

<header>
    <div id="titleDiv">
        <h1 id="bigTitle">OPERA OMNIA</h1>
    </div>
    <nav id="navbar" class="topnav">
        <ul style="list-style-type:none">
            <li><a href="index" id="home">Home</a></li>
            <li><a href="papers.php">Papers</a></li>
            <li><a href="authors">Authors</a></li>
            <li><a href="submit" id="submit">Submit a Paper</a></li>
            <li class="icon"><a href="javascript:void(0);" onclick="dropdown()">&#9776;</a></li>
        </ul>
    </nav>
    <style>
      .topnav ul li [href='authors'] {
        background-color: #d7d7d7; 
      }
    </style>
    <?php
    if (file_exists("banners/". $_GET['authid'].".png")) {?>
        <img id="banner" src="banners/<?php echo $_GET['authid']?>.png" />
    <?php
    }
    else {?>
        <img id="banner" src="banners/banner.php" />
    <?php
    }?>
    <script>
        window.onscroll = function() {myFunction()};
        var navbar = document.getElementById("navbar");
        var sticky = navbar.offsetTop;
        function myFunction() 
        {
            if (window.pageYOffset >= sticky) 
            {
                navbar.classList.add("sticky")
            } 
            else 
            {
                navbar.classList.remove("sticky");
            }
        }
        function dropdown() {
            var x = document.getElementById("navbar");
            if (x.className === "topnav") {
                x.className += " responsive";
            } 
            else {
             x.className = "topnav";
            }
        }
    </script>
</header>