How to adjust transparency of inactive series in highcharter with R

I am using the R package {highcharter} to make a plot similar to this highchart steamgraph.

So far, no major issues. However, I cannot replicate the nice fade animation which occurs with hovering the tooltip.

Bottom line: When I hove over a series, I want the other (inactive) series to fade.

Here is an example of my highcharter plot.

highchart() %>%
  hc_chart(type = "area", zoomType = "x") %>%
  hc_title(text = "Steamgraph of groups") %>%
  hc_xAxis(categories = c("1", "2", "3", "4", "5", "6", "7", "8", 
"9", "10"), 
       tickmarkPlacement = "on", 
       title = list(enabled = FALSE), 
       crosshair = TRUE, 
       labels = list(align = "left", reserveSpace = FALSE, rotation = "270"), 
       lineWidth = 0, 
       margin = 20, 
       tickWidth = 0) %>%
  hc_yAxis(title = list(text = "count"), 
       visible = FALSE) %>%
  hc_legend(enabled = FALSE) %>%
  hc_plotOptions(series = list(
states = list(
  inactive = list(
    opacity = 0.5
  )
)
)
) %>%
hc_add_series(name = "Group 1", 
            type = "streamgraph", 
            data = c(10, 49, 30, 22, 14, 6, 4, 7, 49, 48))  %>%
hc_add_series(name = "Group 2", 
            type = "streamgraph", 
            data = c(54, 12, 82, 42, 12, 6 ,23, 35, 15, 66))

I have tried to adjust the plotOptions but with no success.

Is there a different place to add this parameter?

Thanks