Validating CSS for Joomla! templates can be a difficult task, especially if your template involves parameters for altering the color scheme. For example, in the rhuk_milkyway template, there can be four, five, or more separate stylesheets to validate.
Validating your CSS can be useful to debug any problems with your Joomla! template's presentation.
Firefox's Web Developer add-on (https://addons.mozilla.org/en-US/firefox/addon/60) provides a convenient link to validate the current page's CSS:
When you validate a page on your Joomla! website, you'll see any errors found by the validator:
Where there are errors in more than one stylesheet, you'll see the errors categorized by their stylesheet to allow you to find the errors more easily.
By ensuring your Joomla! template's CSS validates, you can help to prevent bugs or inconsistencies across browsers.