Add correct filename extensions to all of your files

[karlbenedict]

To clarify and streamline testing add the appropriate filename extensions to the files in your site. For example an HTML file (like your DD1 file) should end with a .html extension - yielding a filename of DD1.html. Similarly, all CSS files should end with .css, and javascript files should end with .js. This will both clarify what the files are, and, in the case of the HTML files allow you to double-click on those files on your local computer to open them in your browser for testing.