Base
Base theme is almost a completely clean canvas containing only font icon CSS (no module CSS) and a very basic layout. It is also injected if it is not included in the theme change as otherwise font icons will not work. Any theme built on this will need to include all CSS and possibly overwrite a number of mustache templates and renderers (as these have been built with Bootstrap 3 in mind).
Roots
Roots theme is the best theme to base all other themes off. It has minimal colours and includes Bootstrap 3 CSS along with less files for all components. All core functionality is designed to work with this theme.
Basis
Basis theme is built off Roots with a number of small changes introducing a small aesthetic improvements. It also includes some settings to allow colour changes which may be enough for some instances.
Legacy themes
From time to time we will be deprecating and removing themes as technologies change and improve. It is possible to continue to use these themes after they have been removed by keeping the files in the theme directory, however they will be unsupported and are highly likely to have issues.
Bootstrapbase
Bootstrapbase was deprecated in Totara Learn 9 and removed in Totara Learn 10. This theme was based on the bootstrap 2 CSS framework and does not correctly theme all Totara components. If you were using this as your base theme, we recommend that you convert your theme to use Roots as your new base theme (depending on the level of customisation).
Standard Totara responsive
Standard Totara responsive was deprecated in Totara Learn 9 and removed in Totara Learn 10. This theme inherited from Bootstrapbase, themes all Totara specific functionality and added stylistic information. Depending on the level of customisation, we recommend that you convert your theme to use Roots (if there are substantial changes) or Basis (if there are minor changes).