The option `colorcolumn` is really useful. I would like a similar result to what it yields but only for the two lines that are at the top and the bottom of the screen (*not* the document, but the screen). Is there a way to achieve that?

More generally, is it possible to highlight or colorize a set of positions with row-column coordinates `(row_i, col_i), i = 1,...,N` (again, those coordinates correspond to positions in the visible screen at any time, not the document)?