GeckoFX - How to Highlight a specific HTMLelement ?

I load HTML document in GeckoFX control. Hovering an HTML element (input, select & link) will highlight it with red color, moving mouse out will restore it's visual state.

One idea is to use OnPaint event and draw rectangle at mouse coordinate. 
But I do not know how to use this in C# with GeckoFX control.

Any ideas on how to achieve this or to highlight HTML element are welcome. 

Thank you.