Decal Modification: Solid Rectangle to Rectangle Border?

I’ve created a selection marquee that uses a decal to show the space the player is selecting. I’m trying to change it from a solid rectangle to simply the border of the rectangle, preferably with a constant border thickness. This is what I have right now.

I’ve seen videos where they use a Radial Gradient Exponential, then subtract another with a smaller radius to create a donut-like circle (see below). This is essentially what I’m trying to do but with a rectangle rather than a circle. Any idea how to do this?

Simple math allows to calculate dimensions for rectangle which will be extracted from another to form the border.

Option 1: pixel width of the border

Option 2: percent border, by normalizing on max of width and scale