Class

* The class selector is one of the most popular ways of implementing styles on HTML elements as we can have a subset of elements within the document.
* An example might be: in the CSS styles we would use the selector p.bold then in the body we would put the attribute class="bold" inside the p tag.
* If we use the selector .bold instead of p.bold it then becomes a universal selector which can be applied to any element in an HTML document that has that class name as an attribute, e.g. span class="bold".
* An HTML element can also have multiple class rules, e.g. span class="bold em".
* Writing well structured class selesctors is the key to writing good CSS.