Membership ratio graph Does anyone know how the what the kind of graph in this image is called?

Each color represents a class and the height of the color, in a particular instant, represents the ratio of elements that belong to that class.

How can I produce such a graph, as an example, in R or Python?
This looks like a "proportional stacked area chart." The R Graph Gallery gallery has a similar one here:  

They have great sample sample to provide guidance on how to re-create it (https://www.r-graph-gallery.com/136-stacked-area-chart.html).