Yes, each release of Moodle has core themes and they shouldn't be removed manually or other wise ... just not used.
What version and build date of moodle code is it? That info can be seen in version.php file of the moodle root code.
Shows a 3.6.1+ of code. IF that is your version, you could download and un-archive locally. Find the missing themes in the locally un-archived code/theme/ directory. Upload what's missing to your site using whatever you have as a tool to upload files/folders.
Other supported releases:
https://download.moodle.org/releases/supported/ Moodle 3.5.3+
Security supported only releases:
Legacy releases ... don't think it's these as you said you upgraded not long back:
'spirit of sharing', Ken
Thank you! I will remember this for the next time I screw something like this up, LOL!
But it occurred to me to ask my host (Siteground) if they could restore the files I had accidentally deleted and they did, quite quickly! And everything is back up and running! Super easy solution! AND they showed me how I could do this myself next time with the backup tool that I didn't even know existed before! So YAY for tools that help fix things that I will certainly screw up again in the future!
And I've learned a big lesson! In the future I won't delete anything from cpanel, but will stick with deleting directly from Moodle, as I'm sure it would have not let me delete the themes that would have broken it! But hey, I learned some pretty valuable lessons all around here, so it was not a complete waste of time!
Thanks again! Have a great weekend!
Good! Glad to hear it. Just a word of caution ... account/site backups are only as good as when they were made. Example: so if the last SiteGround account backup was made a week ago and that's what is restored ... yes, the code gets reverted back (problem solved there), but so does the database on an account restore. Moodle sites that are used on a daily basis might now be missing student work. Besides that, there is the database files themselves ... RackSpace, as an example provider, warns that raw copy of files and raw restore of database files are a risk and that they cannot be held responsible when full-filling the customer request should the db files be corrupted. The same is probably true of every hosting provider.
Dodge a bullet? Lucky you! Uhhhh .... safer yet not to be in the line of fire! Strongly suggest setting up a daily sql dump of the database that reside on the server itself. SiteGrounds restore will include those .sql files. So it's kinda like insurance if the raw copy of files gets putzzed at least OP has one .sql file to restore. That suggestion should attract attention of some community members who would suggest taking that a step further.
Bottom line is ... one can never have enough backups ... account, site, and the parts an pieces that make a moodle run ... code + sql dump + moodledata/filedir (last one a minimum).
In many years experience at hosting remotely and running Linux/open sourced apps like a Moodle, never regretted taking the extra time to backup and archive remotely those backups.
Am sure you will have a better/restful weekend!
Good thinking on your part!
'spirit of sharing', Ken