def new_overlay_size(overlay, ratio):
    """
    Determines an appropriate size for the `overlay`, given the image in `start`.
    Currently the overlay will be 1/5 of the width, or 1/25 of the total size.
    Returns a tuple containing the new dimensions.
    """
    overlay_new_width = int(overlay.size[0] * ratio)
    overlay_new_height = int(overlay.size[1] * ratio)
    return (overlay_new_width, overlay_new_height)