<link href="//maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css">
<script src="//maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js"></script>
<script src="//code.jquery.com/jquery-1.11.1.min.js"></script>
<!DOCTYPE html>
<html lang="en">
<head>
<title>Bootstrap Example</title>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css">
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css">
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>
</head>
<body>
<div id="myOverlay" class="overlay">
<span class="closebtn" onclick="closeSearch()" title="Close Overlay">×</span>
<div class="overlay-content">
<form action="/action_page.php">
<input type="text" placeholder="Search.." name="search" required autofocus>
<button type="submit"><i class="fa fa-search"></i></button>
</form>
</div>
</div>
<center>
<h2 style="margin-top:100px;">Fullscreen Search</h2>
<p>Click on the button to open the search box.</p>
<button style="margin-bottom:50px;" class="btn openBtn" onclick="openSearch()">Open Search Box</button>
</center>
</body>
</html>
