[CoffeeLovesYou]

I am having this same issue.
I put

-moz-border-radius: 20px; border-bottom-right-radius: 20px; 
-moz-border-radius: 20px; border-top-right-radius: 20px;
-moz-border-radius: 20px; border-bottom-left-radius: 20px; 
-moz-border-radius: 20px; border-top-left-radius: 20px;

in the Page Background Extra CSS Attributes, however it re-rounds the posts as well on threads.
So, I tried this;

.rounded edges {
-moz-border-radius: 20px; border-bottom-right-radius: 20px; 
-moz-border-radius: 20px; border-top-right-radius: 20px;
-moz-border-radius: 20px; border-bottom-left-radius: 20px; 
-moz-border-radius: 20px; border-top-left-radius: 20px;
}

in the Extra CSS Attributes for Page Background, then I put

<div class="rounded edges">

at the bottom of the header template

and

</div>

at the bottom of the footer template

The result is nothing.

How did you fix this exactly, vijayninel?