Source files for rounded corner pngs?

Thanks for the reply Merlin.

With that in mind, I have gone ahead and done my best to re-produce vector, layered versions of the original corners. I originally attempted to produce fully transparent png's, but found the panels rounded-corner css would have needed significant revisions to make this method work. Additionally, I think some browsers have trouble properly rendering transparencies like the one needed here for the subtle soft effect.

Method:
I did my re-creation in Macromedia (now Adobe) Fireworks 8.

The straight line segments were produced using a 1 pixel, #DFDFDF 'soft line' stroke. The rounded corners use a 1 pixel, #D4D4D4 'soft rounded' stroke and #FFFFFF fill. A drop shadow effect was added to all images to emulate the softened effect with 0 displacement, 15% opacity, and 3 blur.

In retrospect, perhaps a 12-14% opacity on the shadow might have provided a bit smoother transition, but anyone can play with that on their own to suit their personal tastes.

I used Fireworks, not Photoshop, as it is a far better vector design program and allowed more control over how the elements were rendered. Note that although Fireworks uses a seemingly standard PNG file format, it stores layered formatting within that PNG only accessible if opened in Fireworks. Opening the attached zipped PNG's in Photoshop, for example, will provide only a flat image.

Usage:
Each attached Fireworks PNG image has a background layer with a simple solid filled rectangle. Change the color of this item to that of your site background. Click file > export to save it.

For those that wish to use a different panel background color than white (not just a different body background), open the 'corner-bits (fireworks).png' in Fireworks and change the circular path fill to the color desired.

Once you have exported all 5 images with their appropriate names, upload them to:

/sites/all/modules/panels/plugins/styles/corners/

That's it. Hope this helps some of those out there also struggling with the rounded corner theme on non-white backgrounds.

ps. If viewing the attached new-rounded-corners-demo.png, keep in mind the left navigation menu corners are separate and provided by my Acquia theme. I still have to touch those up. But the user profile panels to the right are using the new ones set to match the body background. I'm not sure it's a "perfect" reproduction of the originals, but I think it's close enough. Additionally, as above, I think a slightly lower opacity on the shadow effect might improve it further.