/usr/share/hakyll/example/templates/default.html is in libghc-hakyll-dev 4.9.8.0-1build4.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 | <!doctype html>
<html lang="en">
    <head>
        <meta charset="utf-8">
        <meta http-equiv="x-ua-compatible" content="ie=edge">
        <meta name="viewport" content="width=device-width, initial-scale=1">
        <title>My Hakyll Blog - $title$</title>
        <link rel="stylesheet" href="/css/default.css" />
    </head>
    <body>
        <header>
            <div class="logo">
                <a href="/">My Hakyll Blog</a>
            </div>
            <nav>
                <a href="/">Home</a>
                <a href="/about.html">About</a>
                <a href="/contact.html">Contact</a>
                <a href="/archive.html">Archive</a>
            </nav>
        </header>
        <main role="main">
            <h1>$title$</h1>
            $body$
        </main>
        <footer>
            Site proudly generated by
            <a href="http://jaspervdj.be/hakyll">Hakyll</a>
        </footer>
    </body>
</html>
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