This code enables you to add a unique message after the header on all single posts and pages with a default for all non single pages like achives.
The box spans the full width of the screen and includes a colored background.
Here’s an example:
You can add the content on the single post or page edit screen using custom fields like this:
If you also want to add unique content after the header on archive pages, you can install the ACF plugin which adds a meta box to archives rather than hard code a unqiue message for each type of archive.
Here’s the code for members: