@Rob Wood - <div class=“nav”> is fine (<ul class=“nav” is likely even better!). What I’m really mean is avoiding <div class=“blue”> or <p class=“left”>. Those are non-semantic elements that you’ll want to rename.
@Johanna Bates - I find that the better-structured the code is (and more easily editable it is by other devs later, as well as the more repurposable it is) the more performant it tends to be. You’re right, we don’t have to obsess about selectors as much, but cleanliness of CSS and high performance go hand-in-hand with ease of editing. For that reason I think it’s great to obsess over specificity :) Also, fewer requests is generally better, but sometimes caching rules, asynchronicity and other performance optimizations can impact your decisions about when to make requests.