sitemistic It isnt possible to know the exact article location i.e.to which menu item it is assigned, after viewing the screengrab posted by you. Either, You can provide in direct link from the demo site where the specific article is assigned
Also, Kindly ensure that you have added the css attribute as suggested by Paul, to custom css field or override.css as per documentation here
p {margin: 1em 0 2em;}
and changing margin value accordingly.
Kindly ensure to clear your browser cache also if changes dont reflect