First note… always better to use a child theme to make core theme modifications, but second, to answer your questions ??
1. The rounded corners for the top nav wrapper can be found in the style.css file around line 40. You would change the 60px radius to 0px.
2. For a non-static background, you can find this in the style.css file around line 68 for “body” and change this:
background: #dadddf url('images/patterns/pattern-bg.png') 0 0 repeat fixed;
to this:
background: #dadddf url('images/patterns/pattern-bg.png') 0 0 repeat scroll;
However, this background scroll is only for the lower half. The top half needs to be kept fixed because it’s a special layer that sits behind the main content container (the content part that is above it on top). This one won’t be able to scroll unfortunately due to the design concept. You can remove the styling that is applied to it if you want the actual page background (the bottom half) to show only. If so, let me know and I can show what code you will need to take out.
As I mentioned at the beginning, to make these kind of changes, it’s best to use the child theme method so that whenever Preference Lite is updated, it won’t affect modifications.