Is it possible to thicken the four points of a cell in Calc?

I have created and been using a checklist for something, and I would feel better about it if there’d be no ink where it doesn’t belong, outside the cell. This is what I mean.

It’s just a minor detail, but I would like to subtly steer myself towards making a cross (check-mark) the size of a cell, no more or less, and I was wondering if I could do that in this way.