My goal of learning HTML and CSS is to be able to modify popular scripts such as Wordpress, vBulletin, Drupal, etc. I haven't started yet learning CSS and HTML or XHTML. I see many, many books and tutorials out there so it is difficult to make a choice.

I think most of web designers were like me in the past and have read many books. So, could you tell me about 1 good book for HTML and 1 good book for CSS? and if I should read the book from cover to cover or only learning the basics is enough for modifying Wordpress, for example!