Product review (4 stars): Everyone needs one (or two) of the these
This is such a clever thing, I wish I had one years ago.  It is a strip that fits over that gap between the stove and countertop, preventing crumbs and drips from getting down there.  It has a flap that fits in the gap and a magnetic strip to grip the stove.  It lifts off for cleaning.

It seems to be a standard size.  It is not something you could cut with scissors.

The colors are limited, but perhaps other companies make them in other colors.  My stove and countertop are off white (I think they called the color almond way back when  these are not exactly new), and the gap cap is very, very white.

They are sold separately, so you will need to purchase two if you want one on either side of the stove.