I know the question was already answered, I would like to add an alternative and silly BUT a not really recommended practice since your question does not restrict the answer into being codes...
- Create a blank, square image with your background color as fill, then erase the top-left rounded corners to be transparent, repeat this to all corners
- Set a very unlikely color as your form background color
- Set this color as the
TransparencyKey on your form
- Add the images as
PictureBox and put them to the corresponding corners
Viola!
