This is about the original styles only (orig_* and ohno_*) and does not concern custom styles.
Since NL's Style Manager is effectively the authority on style contents, it's not a good idea for CE to provide tiles which don't exist in the NL versions of those styles.
So, the background tiles that were introduced in CE Version 1.1 RC-1 have now been removed and will no longer ship with CE's copies of the OG styles. If you have copies of these styles with the tiles included, please do not use the tiles in any of your levels as they will no longer be supported by either NL or CE. It's also a good idea to delete them from your copy to prevent any possible confusion, or replace the styles with those from the next CE update (due to be released later today).
If you do wish to use the tiles, they are available in 'special' and 'proxima_tile', from where they will work in both NL 12.14 and CE. The next Editor update (due to be released later today) will make these tiles automatically available from the relevant 'orig' and 'ohno' styles so that it's not necessary to manually search for them. Simply click the Backgrounds button and the tiles will still be there as previously, albeit referenced from the correct style (either 'special' or 'proxima_tile').
Note also that the backgrounds which exist in the NL styles (crystal_level.png, nessy.png, etc) will still be available as before. This topic is only about the colored tiles which were introduced in CE Version 1.1 RC-1.
Meanwhile and on a similar note, the alternative trap animations (https://www.lemmingsforums.net/index.php?msg=107534) will continue to be shipped with CE's copies, but can currently be overridden from Style Manager. If you agree that these updates should be accepted into the OG styles, please show your support by replying to the topic otherwise nothing will happen.