Gradient color fill/opacity in a ribbon between two lines

Hello, I have a graph with two time series(two lines) and I want to create a ribbon in between which will have a gradient fill color or a gradient alpha attribute. For example, I want this ribbon to have an opacity of 60% close to one line and to degrade to 20% closer to the other. I tried geom_ribbon from ggplot2 but as I understood, by searching online this is not possible in R, since geom_ribbon produces a ribbon with only one color or a predefined opacity. Is there a workaround or another way using R, python, etc. to get what I want?    Thank you