page content background color-elements

Greetings,
I am using the latest Pro version of GP and I am trying to create a special page via Elements which will have a background color. Elements itself does not know how to change colors. I searched here via old posts but all of the posts are only about background color around the page but not background of the page itself. I mean changing background color of the page content.
I installed Simple CSS.

I used this for example:

.page-id-997 .one-container {
background-color:#1abc9c;}

.page-id-997 .container {
background-color:#1abc9c;}

But it changed color only around the page but not within the page.
Can you please help?

Thank you in advance