hot to make a block element overlap the page body

Hi there,

please see the url in the private information box.

I created a block element -> generate after header -> and assigned it to the page in the url.
In this test page I created a first container with a blue background.

How can I have the block element slightly overlap the blue container?

So far, I succeeded in vertically positioning them, assigning the page container a negative margin top.
Is this a good way to do it?
And how to have the block element on top of the page? Some z index setting? Where?

I have both GPP 2.0 and generateblocks pro installed.

Thank you for your support. Best wishes. Carlo