When I add a full screen image to a page the text is suddenly shown twice!?

Hello,

when I write a line of text in the edit mode for a page, then that line of text is correctly displayed (only) ONCE in the browser.

Then I would like to put a fullscreen picture behind the text.
I proceed as follows:

a) Via the menu item SIDEBARS I create a Dynamic sidebar for this page.

b) Then I add a featured image to the page and at the bottom of the page I select SIDEBARS -> FULL SCREEN
and then in the pulldown menu I select the Dynamic Sidebar item from a)

c) Via the menu WIDGETS I select CUSTOM QUERY together with the Dynamic sidebar created in a).
Then I choose:
Type: slider
Grid: 1 column
Query: Single Page
Page: the name of the page

The result:
Yes, the fullscreen image is displayed.

BUT the written TEXT is now displayed in the foreground of the picture (as desired) and a SECOND TIME under the on white background in the browser.

Why is the text displayed TWICE in the browser!?