2 minor bugs

1) if the fen position does not have pieces down a file, than the file collapses (it does not happen in boards in pgn

for example use 2r1kb1r/pp4pp/2n1p3/1B2N3/5KbB/P4P2/1P5P/2R4R b k – 0 1

and you will see it breaking along the d file

2) The square_size does not work if you select the pop_up navigation board

Besides those 2 the plugin is really great (and beatiful , which is very important)

https://www.ads-software.com/plugins/rpb-chessboard/