View file htmly-2.9.8/themes/twentysixteen/404.html.php

<?php if (!defined('HTMLY')) die('HTMLy'); ?>
<article class="page type-page hentry">
    <header class="entry-header">
        <h1 class="entry-title">This page doesn't exist!</h1>
    </header>
    <div class="entry-content">
        <p>Please search to find what you're looking for or visit our <a href="<?php echo site_url() ?>">homepage</a> instead.</p>
        <form class="search-form" role="search">
            <label>
                <span class="screen-reader-text">Search for:</span>
                <input type="search" title="Search for:" name="search" value="" placeholder="Search …" class="search-field">
            </label>
            <button class="search-submit" type="submit"><span class="screen-reader-text">Search</span></button>
        </form>
    </div>
</article>