I just finished reading a book I bought one year ago. I found the book very dry at first, at least the first chapters, so I had put the book aside for many, many months... If writing CSS is a main part of what you do, you should get this book. It will confirm most of what you've acquired in knowledge through reading from a hundred different sources and from hard work over the years. But no matter how well you think you know your stuff, you will learn new extremely useful concepts and patterns. It's not about learning the cool tricks of the day, it's about becoming able to do Whatever Whenever, it will give you ultimate control in pretty much every situation. Don't worry, the book is not accessible to those who do not have the Capacity, it will only embrace the Deserving. It is like a Kabbalah or Secret Book of Knowledge, you must be ready for it, and you must be serious. Chances are... if you read this, you're ready and able... and willing. You may already own the book if you tend to buy everything that's ever published on CSS. Grab it, read it.
The book is Pro CSS and HTML Design Patterns.
The author is a musician. From the preface: “Michael is also an accomplished pianist with a bachelor’s degree in music composition, a master’s degree in music theory, and an ABD PhD in music theory. [...] In his spare time he loves to improvise, arrange, and compose music.” If I may use an analogy... If you read this book, you will no longer play CSS by ear, you will learn to read and write CSS music. You will be able to not only replicate but combine patterns into novel ways. There's nothing wrong with playing CSS by ear, and applying recipes, a lot of people have figured out how to do stuff that we tend to do over and over again... most web designers will never go beyond applying recipes, and relying on CSS frameworks, their own or others'.