The id selector uses the id attribute of an element to find a specific element on the page — as you probably remember from our HTML course, ids can't repeat on the same page. To select the element by its id, use a hash (#) before the id's value — for example, #header.

You might want to add element tags just to let yourself visually know in your CSS what you are targeting. For example, if id="header" is applied to the container <div>, you can use div#header as a selector.