There are three CSS files in the default theme. They are named theme.css, admin.css, and admin.styles.css. Just from the names, we can guess that the last two files are related to the backend administration. That's indeed the case. However, since it is possible to put the administration function on the frontend (this is a setting in the VirtueMart configuration), so the admin stylesheets are also placed under the default, so that you can customize it to fit your frontend needs. While it is possible to use the administration modules in the frontend, they are not the norm. So we will not go into the detail of the admin stylesheets here. We will look at the theme.css in more detail below.
There are close to 100 different stylesheet definitions in the theme.css file. Most of them are defined for class. Because of the cascading nature of a stylesheet, it is best practice to link the styles to class (or ID) instead of tags. Otherwise, the styles may overflow to other...