Using same corner radius setting for both outer and inner rounded rectangles will create a “lump” corner like an eaten mice in snake’s stomach.

Mmm, mice!

Radius number should always be lower for inner box. In measurement example picture above, I used 14 px for outer box, 8 px for inner box to create a perfect size border all across the corners.

Photoshop’s Rounded Rectangle Tool Setting.

Side Tip: Enable ‘Snap to Pixels‘ in option box if you want box to be sharp instead of loose like vector. Leaving it unchecked will make the box blurry when rasterized.

Image below is an example of widget box my brother designed with incorrect radius setting:

While average Joe will not notice this, it’s something that all graphic designers should know. It will make your work look more professional and accurate.