Can anyone please tell me what went wrong and how I can fix it?
Also, is there anyway to go back to 7.8.22 version. I have no backup as I didn’t really have any data.
In worst case, I could install the complete package of 7.10.9 from scratch but I would like to understand what happened.
There is no “uninstall” or “roll back upgrade” option. That’s why a backup is explicitly recommended on the upgrade screen, and a test upgrade on a clone also.
Your problem shouldn’t be too complicated to solve, anyway. It simply looks like your CSS is broken. Maybe this can be cleared up with a “Quick Repair and Rebuild”, or if not, then it’s probably caused by wrong ownership/permissions settings, which you can correct (there are instructions in the installation Docs, and in many threads here on the Forums).
If you have trouble navigating the menus to get to the Repair screen, temporarily use your browser settings to not use any CSS. In Firefox this is “View” menu, “Page Style”, “No Style”. There is a similar option on other browsers, surely. Revert this setting after you run the QR & R.