The problem is that the box inside the one with border radius does not have a border radius of its own, so it's busting out of the radiused container. Add a border radius to the internal box with the background image / colour of one pixel less than the outer box, and it will work fine.
The problem is that the box inside the one with border radius does not have a border radius of its own, so it's busting out of the radiused container. Add a border radius to the internal box with the background image / colour of one pixel less than the outer box, and it will work fine.