Thumbnail display error and how to round thumbnail corners

1. When I choose 8px rounded corners, only the large image has rounded corners but the thumbnail does not have rounded corners, only the first and last images in the thumbnail are missing 2 corners like the attached image (this missing I see it as a bug), but the image in the middle is still square, how to apply 8px rounded corners to both the large image and all thumbnails at the same time

2. How to apply border to thumbnail like the attached image