Hi there, I'm Matt Sergei (do call me Matt, please) and will create a javascript function and demo web page where:
1. A function call with a point and polygon lat&lng coordinates will return true or false.
2. The polygon will be displayed with transparent overlay on the OpenStreetMap, implemented with LeafLet javascript library.
3. Points will be added as markers on the map, with say green if inside the polygon and red if not.
Please let me know if this would work for you.
Regards and hope you're safe,
Matt