Styling a sudoku grid

Question

I’ve created a sudoku puzzle creator / solver and need a bit of help with some CSS to style it.

Typically they are styled like this:

.

Some naming I’m us

Answer 1

If it were me, I would have used a table with 9 rows and 9 columns.

Then used :nth-of-type(3n) in the CSS selectors to set the border on every third row and column.