Modify opacity of background map

[juanmed]

I am using mplleaflet to display an scatter of points in a map. Is there any method to decrease the opacity level of the background map? So far I have achieved it manually by modifying the leaflet.css file line 137 "opacity: 1;" to the value I want, 0.5 for example. However I need to create a huge number of maps so setting it manually is not practical.

I also tried passing the alpha argument when creating the axes on the mpl figure, but does not work. The alpha value for each point I draw does work. But I want to modify the opacity for the base map, not the points I am drawing.
I also tried modifying the CSSLink directing to the leaflet.css file. I made my own copy of the file with the (fixed) value of opacity desired, however it does not work since the map construction with the new CSSLink is not correctly rendered.

Any help will be appreciated.