Getting rid of top and bottom page space

Hi, I need to get rid of top and bottom page space on this page: (red colour)
Theme: Coursepress with child theme - no amendments, just a copy of original style.css
Plugins: Divi Builder, Blank slate.
I am using Divi Builder plugin as a page builder to create a page on Coursepress theme. And I am using Blank slate plugin (its blank page template) on that page to get a blank page so only the content of the page is displayed. I am getting unwanted space at the very top (5px) and the bottom (30px). I put a red Background for better demonstration.
CSShero generated the following css:

body {
margin-bottom: -30px!important;
margin-top: -5px!important;
padding-bottom: 0px !important;
padding-right: 0px !important;
padding-top: 0px !important;

and it looks good on a preview, but ones saved - red gaps are comming back. I was trying to amend style.css unsuccessfuly. Any help appreciated.

P.S. Ideally the amendment would be within the plugin Blank slate, in it's template file blank-slate/blank-slate-template.php , this way other pages that are not using this plugin will not be affected

P.P.S. Could you please move this ticket from General to Coursepress specific