Difference between #id and div#id

Question

I am new to css. Can someone help me in differentiating \"#test\" and \"div#test\"?

Answer 1

You really ought not to qualify an ID with a tagname per the MDN, as follows:

Don’t qualify ID rules with tag names or classes

If a rule has an ID selector as its key selector, don’t add the tag name to the rule. Since IDs are unique, adding a tag name would slow down the matching process needlessly