UPDATED: August 27, 2020 by @stpaultim

Possible solutions: * issue #4512 - Supplemental stylesheets * issue #4782 - Supplemental CSS selectors

Description of the need

A new user that does not have the time or skills to create their own theme or sub-theme should be able to build a solid, reliable, and functional site without need to install a contrib theme. However, there are a number of small problems with Basis that make that difficult, some of which have been fixed or are in the process of being fixed.

Most Backdrop developers are used to creating custom themes for sub-themes for their sites and routinely deal with these issues during that process OR have created their own sub-theme templates with fixes in place.

It is my concern that as we continue to tweak Basis and/or fix bugs, that we might end up breaking or making unexpected changes to existing sites that are using Basis as their only theme. Since we are at least 3 years away from Backdrop CMS v 2.x, I would like to decide on a best course of action for providing a robust and flexible theme (for beginners with limited theme building skills) in core that can safely be used "out of the box" and will accommodate a variety of uses.

Possible solutions that have been considered

1) We could go on making updates to the current version of Basis at some risk of minor breaks to sites that are already build using Basis out of the box without any sub-theme or changes. 2) We could introduce Basis v 2.x into core as an experimental theme, making it clear that it is under development until 1.x-1.16.x (or whichever version we determine) 3) https://github.com/backdrop/backdrop-issues/issues/4167#issuecomment-554... We could develop it as a contrib theme, but with an expectation that we eventually moving it into core at a later date. We already have https://github.com/backdrop-contrib/basis_contrib 4) Issue #4512 - Add a "supplemental stylesheet" to Basis (or default theme) that includes new css or overrides that might cause problems with existing sites. This "supplemental stylesheet" would only be used if a config option was checked, the default would have this config off, but on new sites it the install profiler would turn it on. [Added 10/28/19 - inspired by discussion here: #4166] 5) https://github.com/backdrop/backdrop-issues/issues/4167#issuecomment-666... Create and add a sub-theme of basis to core called something like "basis_edge" or "basis_current" that includes all the changes. This new sub-theme would be the default theme on new sites, but old sites would continue to rely on the existing version of basis. 6) https://github.com/backdrop/backdrop-issues/issues/4167#issuecomment-667... Create a new default core theme, keeping Basis as it is but deprecated, and try to fix as many of the issues as possible in this new core theme. (This is very similar to option 2. It's not clear if either of these plans offers an avenue for ongoing improvements in CSS). 7) Issue #4782: Add support for supplemental CSS selectors. All new CSS or CSS overrides that might cause problems with existing sites would be prefixed with a class matching the version of core where it was introduced. That class would only be added to sites installed on or after that core version. 8) Issue #5175 : A new theme to core - This may be the most ambitious option. The idea is that if we cannot find another way to fix CSS issues, we could simply create a new theme for core that fixes existing problems, is updated to give Backdrop core a new look, and possible contains within itself a system that allows updates and fixes safely.

Some Issues blocked by this decision

Additional information

This idea was inspired by issues such as:

[META] Issues with Basis https://github.com/backdrop/backdrop-issues/issues/4094

Should we set default margins on 'p' tag in Basis? https://github.com/backdrop/backdrop-issues/issues/4166

Remove the hover color from header account links in Basis https://github.com/backdrop/backdrop-issues/issues/3748

Basis & Flexible Layout Templates: Remove white space between two hero blocks placed next to each other. https://github.com/backdrop/backdrop-issues/issues/4095

I really don't know if this is a good idea or if it's necessary to accomplish the goals I've outlined, but I wanted to put it out there for discussion.

GitHub Issue #: