CSS: The class selector

The class selector is a way to select all of the elements with the specified class name, and apply styles to each of the matching elements. The selector must start with a period (.) and then the class name. The browser will look for all tags in the page that have a class attribute containing that class name.

The spelling and casing must be exactly the same - ".cold-city" is different from ".Cold-City". The class name can't contain a space, but it can contain hyphens or underscores. Any tag can have multiple space-separated class names.