CSS: The id selector

The id selector is a way to select only the element with the specified id, and apply styles to that element. The selector must start with a pound sign (#) and then the value of the id attribute. The browser will then look for a tag in the page that has an id attribute equal to that id.

The spelling and the casing must be exactly the same - "#sun-descrip" is different from "#Sun-Descrip". The page should not have multiple tags with the same id- every id should be unique.