[samgro]

Any "CSS Best Practices" guide should start with "1. Use a preprocessor."

Also, don't use IDs? Really? The article referenced as a source for this claim ends with "Don’t stop using IDs, just be aware of where they can cause you headaches and know where to sensibly circumvent them. Anyone telling you not to use them at all is not wrong, but they’re definitely not right…"

That's good advice. Understanding how specificity works will make you realize, when designing your Twitter widget, relying on a selector ".tweet a" is unreliable, and use "a.tweet-link" instead.