ID vs CLASS in CSS. Please explain in detail with example

Question

I have heard that ID is unique and can only be used once in a page, but its working fine when used over multiple times on a page. Please let me know the purpose of ID and hows i

Answer 1

In CSS terms, ID's are faster to find than classes.

You should use classes for things that are to be re-used.

EG:

@CSS

.displayNone
{
    display:none;
}