This is not critical and easy to fix but I suppose it should work right out of the box.

If you set a dark background color to the modal-header there will be white space between the border of mobile-content and modal-header.

This is a zoomed example:

There are several options to fix but I'm not sure which one is the best.

For now, I use this "fix"

.modal-content {
  overflow: hidden;
}

.modal-header {
  border-radius: 0;
}