This book not only explains how to do write in XHTML and CSS but it tells you why the W3C has changed its standards and why you should write in these two recommendations. It gives you thoroughly explained examples, and explains it in different ways to make you sure that you get it in case you didn't the first time.
This is an easy book to read but it takes some time as it educates you about related topics that you might want to know about.
Not only do you get to learn XHTML and CSS but you also get to update a website the publisher provides to put your new skills to practice and make sure you get it in your head. It also makes a good reference book as it explains CSS properties in detail and their values.
Now adays accesibility is a key tool for websites and that's what you'll learn at the end of the book.
I recommend this book to anyone who already knows HTML and has written websites in HTML (if you dont, dont buy this book to start with) that is willing to take their skills to the next level.