Overlay_elevation example is broken

[antipenultimate]

(video) C:\Users\antip\Documents\GPXOverlay\examples>python overlay_elevation.py
Traceback (most recent call last):
File "overlay_elevation.py", line 14, in
main()
File "overlay_elevation.py", line 9, in main
elevation_overlay = overlay.Overlay('sample-data-short.gpx', 'video.mp4')
AttributeError: module 'GPXOverlay.overlay' has no attribute 'Overlay'

Win10, python 3.8. Other examples work.