Class and ID Selectors. For the CSS Beginner Tutorial we looked solely at HTML selectors — those that represent an HTML tag. You can also define your own selectors in the form of class and ID selectors. The benefit of this is that you can have the same HTML element, but present it differently depending on its class or ID. In the CSS, a class selector is a name preceded by a full stop (“.”) and an ID selector is a name preceded by a hash character (“#”).