Trying to create crossword, can't block a cell black

I’m working on a making a template to build crossword puzzles. I need to black some cells in a table. [Not background] Anyone know how this is done?
[Have been using tables in Writer, perhaps Draw is better.]

Why “Not background”? I think this is the easiest solution. (I say about Calc table now)

Try to create a crossword puzzle in Calc. Example and instructions attached.Simple sample of crossword.ods

No, you can’t block individual cells of a table in LibreOffice Writer. The only option is make black colour background.

Maybe easy to do in a spreadsheet.