As a high proportion of VirtueMart users do not use the standard default theme, or have already extensively edited the default theme, it is not possible to always be specific where any style or layout edits should be made. This tool enables you to work this out for yourself.
Most Joomla! site developers use the Firebug tool in Firefox to examine displayed pages, to show page HTML and CSS code, and to test the effects of changes within the code. This is a very good tool for the rapid identification of VirtueMart template layout issues and the dynamic testing of changes to CSS - without making any actual alterations to the underlying code.
Having identified any required alterations or additions in CSS, those changes can then be written into the relevant CSS files in the Joomla! template or VirtueMart theme CSS.
To see an introduction to the use of Firebug see http://docs.joomla.org/Tutorial:Using_Firebug_With_Your_Joomla_Website
and Firebug documentation here: http://getfirebug.com/wiki/index.php/Main_Page
You could also use Chrome's developer tools - maybe with Firebug Lite. - https://developers.google.com/chrome-developer-tools/docs/overview