Joomla 3 Page Class text boxAt this writing, the Protostar Template is not written to recognize Page Classes as assigned in your Menu Item under the Advanced Options -> Page Display options -> Page Class. 

It is a great styling tool to be able to add a class to the entire page.  It allows you to style elements for that page alone without affecting all the other pages on your site.

In order for Protostar's Template to recognize this setting you must make two additions to your index.php in the template -> protostar folder in your Joomla 3 files on your hosting company server. Do not modify the index.php right on the root directory.  You are only modifying the one in the Protostar Template folder.

1: Make a copy of the current index.php file - rename the copy to something with the date in it, for example: index6-4-13.php.  This way if you have several index___.php files you will know which one is most recent.

2: Open up the index.php file in a text editor like Notepad++. 

3: Add this code inside the <?php ?> section above the <!DOCTYPE html>.

$app = JFactory::getApplication('site');
$pageclass = & $app->getParams('com_content');

Note this code is written in PHP - it must be placed before the closing ?> symbols.

4: The body tag already has a number of class parameters added, but you need to add two more lines to get the page class to be added as well.  The final <body> tag should look like this:

<body class="site <?php echo $option
    . ' view-' . $view
    . ($layout ? ' layout-' . $layout : ' no-layout')
    . ($task ? ' task-' . $task : ' no-task')
    . ($itemid ? ' itemid-' . $itemid : '')
    . ($params->get('fluidContainer') ? ' fluid' : '')
    . (' ')
    . ($pageclass ->get('pageclass_sfx'));

Note: Be sure that you have the semi-colon only at the end of the last line since this really is only one PHP statement that has been concatenated.

5: Go into your Menu Item in the Joomla 3 Admin Interface. Assign a Page Class under Advanced Options -> Page Display options -> Page Class, for example "aboutpage". 

6: Bring up that page in a browser window (or refresh the page) and look at the Source Code using Firebug or something like that. You will see the page class added at the end of all the other classes on the <body> tag.

<body class="site com_content view-article no-layout no-task itemid-119 aboutpage ">

Now you can add specific styling in your stylesheet for elements on that page. For example:

body.aboutpage {color: #fd6734;}