Changing the outline colour of BarLegend

I have a ListDensityPlot with argument PlotLegends -> Placed[BarLegend[Automatic], Below]. It produces an output like the following:

Can an argument be passed to BarLegend that changes its outline colour? In particular, I want it to be Black, rather than Gray.

• try Placed[BarLegend[Automatic, FrameStyle -> Black], Below]?
– kglr
Sep 23 at 6:11
• @kglr many thanks - this works. I get an 'unknown option name' warning when I do this, though. Any idea why? If you want to write your comment as an answer I can mark this question answered. Sep 23 at 12:46

Follow the advice by @kglr, we use PlotLegends -> Placed[{FrameStyle -> Directive[Black, Thick]}, Below] since the default legend of ListDensityPlot is the barlegend.
ListDensityPlot[