Of course they don't put their money where their mouth is and the document that describes this guideline itself doesn't follow it:

    <!DOCTYPE html>
    <html lang="en">
    <head>
    <meta charset="utf-8">
    <title>Google HTML/CSS Style Guide</title>
    <link rel="stylesheet" href="javaguide.css">
    <script src="include/styleguide.js"></script>
    <link rel="shortcut icon" href="https://www.google.com/favicon.ico">
    <script src="include/jsguide.js"></script>
    </head>
    <body onload="initStyleGuide();">
    [...]
    </body>
    </html>