I’ve tried four plugins that are supposed to make a sidebar — or a widget — sticky. None have worked. I’ve also tried a plugin that is supposed to add a notification at the top of the site; that didn’t work, either. Does anybody have a suggestion?
Adding notifications at the top, over the content or at the bottom of the site should work with any theme if the plugin is correctly coded. Try a different plugin if the one you used seemed to not work.
The theme’s sidebars are not designed to be sticky – achieving this with a plugin will most likely not be possible (since the plugin cannot take into account any theme’s possible styling). This should be possible with custom styling, but it is not an easy task (also, the “stickyness” behaviour is variable)