Using a Chrome extension with Slimjet (GetCRX), I can pack installers for extensions and themes from their Chrome pages. The extension installers so packed will install into Opera. Opera refuses to install the themes, however.
@flynn-farrow I can, but opera do not allow me to setup custom search engines as default, so i have to assign a letter and press that letter first everytime i search, as i said, is a minor incovenience but i do not want to do it this way.
Brave and Vivaldi already have other search engines available to be default, the fact that opera do not allow this is a little concerning to me.