Users reported a bug where navigating back from the ‘Edit Code’ section in theme components redirects to the old UI (admin/customize/themes/28) instead of the new one (admin/config/customize/components). j.jaffeux confirmed the issue, noting the sidebar appears incorrectly after using the back button. JammyDodger reproduced the bug and noted that admin warning links also point to the outdated interface, suggesting all UI links should direct to the new ‘config’ version. Jagster added that even viewing custom CSS/JS triggers the issue, and mentioned the old UI remains useful for bulk copying theme components between forums. sam acknowledged the issue as high priority, promising a fix soon. The bug was ultimately resolved via PR #32875, as confirmed by kris.kotlarek.
I don’t think the old style of the theme/theme component page should be accessible through a UI link anywhere? I think they should all point to the new updated ‘config’ version.
I think the links on the admin warnings also send you to the old style as well.
For me there is no need to edit custom css/js. Just opening it is enough, if there is any code.
(I actually used it yesterday. We don’t have any easy way to import/export theme components is bulk to new forum. Old menu is very much easier to copy and then create in the new forum )