The redmine-a1-theme theme has been updated. New version improves compatibility with Redmine 4.0 and adjusts styles of form inputs.
The theme can be downloaded from GitHub. You can install/update it by extracting theme directory into
public/themes/ (final path to style sheet file should look like:
public/themes/a1/stylesheets/application.css) and enable it in Redmine admin panel. The theme is compatible with Redmine 4.0 (it should work with older versions of Redmine, but it was never verified).