I wonder if it could be Elementor doing that. It doesn’t show on every page.
If I turn off Elementor temporarily will I permanently lose my designs or will they come back once I turn the plugin back on? Sorry if that’s beyond your scope, I just don’t want to break anything while trying to get rid of that bar.
The CSS is coming from Send In Blue – not something you can edit as its coming from another server. You may want to report it to them as its bad practice for them to install very generic CSS – it should be specific to their code requirements