(For users who’ve bought the Custom Design upgrade)
Where is the CSS of the theme?
You can view the original stylesheet if you
go to Appearance > Custom Design > CSS, [see Update below] click “Edit” next to “Mode: Add-on” in the Publish module, and click the “theme’s CSS” link:
You can also view it here (click name of theme then click “style.css”):
Update April 11: WP replaced the regular CSS editor with a narrower new editor in a black overlay sidebar over the blog preview. Το access the old CSS editor (including the module shown above), visit your main dashboard screen and change its URL from:
BLOG URL HERE/wp-admin/
BLOG URL HERE/wp-admin/themes.php?page=editcss
(You can bookmark the page, so that you won’t have to enter this URL each time you want to visit the editor.)
Why is the stylesheet hidden like this?
When the link to the CSS of the theme was more prominent, inexperienced users would often copypaste the entire stylesheet into the CSS editor and start making changes to it. This a mistake: at best, it makes browsers unnecessarily read the whole stylesheet twice; but it can also create conflicts, because what takes precedence over what is very complicated. You can copy the original stylesheet and save it in a text file for reference, but you don’t copypaste it into the CSS editor (if you don’t like wondering why this or that didn’t work).
How do I make CSS changes on wordpress.com?
Unless you are an expert user who wishes to make very extensive changes, you retain the default edit option, i.e. the add-on mode, [Update: in the new CSS editor you do not check the option "Don't use the theme's original CSS"] and you enter only the selectors for the elements you wish to modify and only the rules for the properties & values you wish to add or override (after deleting the welcome message, of course). Apart from avoiding redundancies and possible conflicts, this also allows you to keep track of the changes you make, and remove or modify any of these changes without fearing you might mess the original.
The original stylesheet of a certain theme includes this:
If you wish to make the post titles a bit larger and italicized, the only thing you’ll add in the CSS editor is this:
When you wish to apply the same change to various elements, you can combine the respective selectors. For instance, if you wish to italicize the blog title, the post titles and the post metadata in the above theme, you add this:
Selectors vary from theme to theme, and so does the structure of each theme. In addition, the less than elementary changes may require some inventiveness. For these reasons you shouldn’t expect to find manuals that give you simple, direct, one-size-fits-all answers to how-to questions. You need to familiarize yourself with the various CSS properties and their possible values, but you’ll always have to examine the particular situation in the particular theme you’re using. To examine your blog and identify elements, selectors and rules, as well as try out changes, you can use the Firebug add-on in Firefox, or similar developer extensions in other browsers.
You can also learn a lot in the wordpress.com CSS forum: you can study replies in general, search for a past reply to a specific question, and post your own questions. Note that users who’ve bought the Custom Design upgrade are entitled to staff support. Also note that replies in the CSS forum generally assume that you’re using the CSS editor as recommended.