Snake - How to make a line of the edge of the screen with a grid??

well, I made a little snake game for android. and it is doing alright,
but one thing i want to add is a line around all the 4 edges of the screen.
so the snake cant go out of the screen, and die.
I think i can make the die symstem by my own but how to i make a line on the edge of the screen.
my grid size is 48 so i want the width of the line 48.

someone any ideas??

What about making a dot like image in Paint and then you can scale it 48 on X in Unity?