Theme Style Variations
A theme may have multiple style variations by using one or more separate sets of css stylesheets which will be used to override the default styles. Even though only one of these styles may be active at a time, it makes it easier than creating an entirely new theme and is contained in the same theme folder.
The default theme style sheets are stored in the 'css' folder inside the theme folder. These are the style sheets used by default. To create a style variation named 'stylevariationname', create an additional folder with the name of 'css_stylevariationname' and place the style sheets used to override the default styles (which are still used) there.
To select a theme style variation, use the 'Theme Manager' which displays any style variations to the theme if found.