If you use Apache, then you most likely have DirectoryIndex enabled on your development server. This is the feature that lets you request a directory without a home document and see a list of folders and files. This is notnormally enabled in production, but in certain circumstances it may be. (For a file download directory perhaps.) If you do any testing with mobile devices though you will probably find this index to a be a bit hard to read. Here's an example.

You can pinch and zoom to make that a bit easier to read, but it's a pain in the rear. Turns out Apache has a few options that allow you to customize how this index file is created. One of them, IndexHeaderInsert, allows you to add HTML to the head section of the document. I added the following to my Apache httpd.conf file:

IndexHeadInsert "<meta name=\"viewport\" content=\"width=device-width, initial-scale=1\">"

And the result was exactly what I needed:

Hope this helps!