This section provides guidance on developing themes for Backdrop CMS

A theme is a collection of files which define the presentation layer of a Backdrop site. The theme determines the appearance of a site including fonts, colors, backgrounds, and other decorations.

In Backdrop, themes are not responsible for the layout of your site. For example themes have no say over the number or arrangement of columns available for your content.

You can also have one or more "sub-themes", or variations on a theme.