Plugin Icons not showing in Leaflet using R

Hello,

We have a need to use a mapping solution in PowerBI embedded. Since neither of ArcGIS or MapBox works for us, we are creating a mapping custom visual using Leaflet and R in PowerBI. For the most part, the visual works fine, but whenever we are trying to add a leaflet plugin, the icons for the plugins do not show up in the visual.

Here's how the 'Measure' plugin should look (RStudio)

And here is how the icon looks in PowerBI visual

I'm really not a coder and certainly not conversant with .js, hence our inclination towards using the Internactive R visuals to create the Leaflet visual.

Making custom Interactive R visuals with PowerBI indeed opens up a host of possibilities in PowerBI. Any help on how to rectify the issue is most welcome. 

Best Regards,

Jigar