Question

I have a div with an ID:

<div id="main">

What’s the correct (or difference) between

div#main {

and

#main {

Regards,

Answer 1

There is a great doco on using efficient CSS selectors, focus on rules with overly qualified selectors:

ID selectors are unique by definition. Including tag or class
qualifiers just adds redundant information that needs to be evaluated
needlessly.

Instead of just applying the style to an element with id main, your selector will re-qualify the element by checking whether or not it’s also a div (in that order). To clarify: css selectors are evaluated right to left, unlike same selector syntax when used in jQuery etc.

Re pixelistik’s suggestion that div#main is more specific than #main – yes, that is technically correct, however if you have to resort to this to raise a rule’s specificity, chances are the structure of CSS you’re working on is not as thought through as it should be.