With your project closed, try opening up your .css file
(default.css unless you created a new one) in a text editor like
Notepad. Under BODY, enter a line like the following (this example
declares the left margin):
margin-left: 20px;
Enter whatever value you want. You can also set margin-right,
margin-top, and margin-bottom values. If you want all margins the
same, use:
margin: 20px;
...with your own value instead of 20.
When you open your project, you should see the new margins in
the WYSIWYG editor. I haven't seen RoboHelp change styles that I
have manually entered in the .css file, so this should stick.
--Ben