You can use the extra style hooks provided by swiss_2.js as introduced here:
To get the exact positioning you want, you may need to put a div on the page and move the controls into it. Here's an example of that:
Use your browser's 'view source' to get the code. That was made as part of this thread:
Reading it might be of help to you.
About styling the buttons - the border is actually a hover background color and is set using the button_highlight property of the slideshow. For no highlight, use the background color behind the image buttons or set it to transparent, examples (for over an area with a white background):
Or for blending in with any background:
slides#.button_highlight='#ffffff'; // onmouseover background-color for image buttons (string) (requires image_controls=1) - use color name or hex value with # prefix