I am running Ubuntu Bionic Beaver. I was trying to download the pantheon desktop environment on Ubuntu and it didn't work so I gave up. Now when I try to download themes or other things from the terminal I get an error code mentioning Elementary OS even though what I am downloading doesn't have to do with Elementary or pantheon. Here is what the terminal says:
jacob@jacob-MacBookPro:~$ sudo apt-add-repository ppa:tista/adapta -y
…
E: The repository 'http://ppa.launchpad.net/elementary-os/testing/ubuntu bionic Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: The repository 'http://ppa.launchpad.net/mpstark/elementary-tweaks-daily/ubuntu bionic Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.