[z3t4]

In the classic days of web dev it was best practice (and still is in my opinion) to separate style (CSS) from functionality (JavaScript). So you had classes for CSS and id's for JS. So if you change the id you don't have to update your CSS. If you have a "singleton" it's better to use the element's name instead of id in the CSS. for example body instead of #body for the same reason (separate from JS). And if you want to have different types of body, add a class to the special body. id's will for example create global JS variables, so if you are styling using #id you will create a bunch of unnecessary global JS variables.