This is a paragraph styled with an id selector. Ids are required to be unique. The idea is that each usage of an HTML element has a unique identifier. However, a browser will render a page where two elements have the same id. JavaScript and other APIs will not work correctly unless the id is unique. Thus, an id selector is just like a class selector, except that it can only be used once per page.

This is simply a paragraph with default paragraph styling. Nothing fancy going on! Your browser made all the decisions.