Welcome to the world of HTML styling!
CSS lets you change the values of many different visual properties elements on your web page.
When a web browser reads an HTML page, it internally reperesents it in a tree-like structure called the document object model, or DOM for short. CSS rules are applied to the DOM.
Note that the previous paragraph is a different color. It uses an inline style to set the color of the paragraph to green. The inline style over-rides the internal style rule from the head.