Scott Reilly

This plugin provides template tags that allow you to retrieve the name, path (relative or absolute), url, or fully marked-up link to a randomly chosen file or files in a specified directory.
Arguments to the functions permit you to limit what file(s) can be randomly selected based on a given set of file extensions. You can also explicitly specify files that should not be randomly selected.
This functionality can be useful for displaying random images/logos or including text from random files onto your site (writing excerpts, multi-line quotes, etc). Other ideas: random ads, random CSS files, random theme template selection.
Notes:
<ul>
<li>
If you want to actually display the name of the random file, be sure to ‘echo’ the results:

</li>
<li>
Unless you limit the file search to only include a particular extension (via <code>$extensions</code> argument), all files in the specified <code>$dir</code> will be under consideration for random selection
</li>
<li>
Can be run inside or outside of “the loop”
</li>
</ul>
Links: <a href="https://coffee2code.com/wp-plugins/random-file/" rel="nofollow ugc">Plugin Homepage</a> | <a href="https://wordpress.org/plugins/random-file/" rel="ugc">Plugin Directory Page</a> | <a href="https://github.com/coffee2code/random-file/" rel="nofollow ugc">GitHub</a> | <a href="https://coffee2code.com" rel="nofollow ugc">Author Homepage</a>
<h3>Developer Documentation</h3>
Developer documentation can be found in <a href="https://github.com/coffee2code/random-file/blob/master/DEVELOPER-DOCS.md" rel="nofollow ugc">DEVELOPER-DOCS.md</a>. That documentation covers the template tags and hooks provided by the plugin.
As an overview, these are the template tags provided by the plugin:
<ul>
<li><code>c2c_random_file()</code> : Retrieves the name of a random file from a specified directory and returns information based on the file.</li>
<li><code>c2c_random_files()</code> : Retrieves the name, path, or link to a specified number of randomly chosen files in a specified directory.</li>
</ul>
These are the hooks provided by the plugin:
<ul>
<li><code>c2c_random_file</code> : Filter to safely invoke <code>c2c_random_file()</code> in such a way that if the plugin were deactivated or deleted, then your calls to the function won’t cause errors in your site.</li>
<li><code>c2c_random_files</code> : Filter to safely invoke <code>c2c_random_files()</code> in such a way that if the plugin were deactivated or deleted, then your calls to the function won’t cause errors in your site.</li>
</ul>

Random File

Retrieve the name, path, or link to a randomly chosen file or files in a specified directory.

flocsy

Customize Randomize CSS plugin to fit any other WordPress plugin or theme 
and randomize colors in your blog.

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Randomize CSS plugin can be configured to randomize part of the css on each page view. It can for example change random colors.

Random File vs Randomize CSS