why are css id selectors bad?

[iffyuva]

i was going through this: http://markdotto.com/2014/07/23/githubs-css/ and found this statement: "We’re aware of bad practices—over-nesting, IDs, elements, etc"

can you point to any good article/blog which throws light on this?

[mdo]

They're not inherently bad, they're just bad for building reusable things in CSS because and ID means one thing. Classes are used so that you can reuse and extend without incurring overly specific CSS (and ID is more specific than a class). Plus, classes enable you to use an element more than once in a single page.

[iffyuva]

thanks for making it clear.