I'm always weary of online tutorial websites that teach you how to effectively write HTML/CSS. Although the bios of the authors often refer to the amount of time they've spent working in the web industry, neither does it refer to the type of exposure they've had to different projects, nor does it mention their intentions.
If I were to develop CSS with a strong focus on browser compatibility, it would be far different from developing it with a focus on browser performance (read: Steve Souders). The same goes for CSS intended for longterm use and CSS written to support accessibility. These things are all different.
Websites like Smashing Magazine offer great tips on how to approach the technical issues inherent with web development, but the tutorials should be seen as just that; references. There's no such thing as a one-solution-fits-all. If there was, it would probably be one that far exceeds any clients' budget.