(Need Help) 2 Images to resize responsively together. (on top of one another)

I am using this image as an example. I wish to set the floor plan image as the background in Editor X (Full screen). The I place the gif of the location pin on the image. How on earth do make the pin (as an example) stay on that box no matter the screen size?

I've made 4 break points and sized to that, but there are screens in-between and when I drag the side bars it floats. Driving me nuts. Would be SUPER greatful for any advice.

Thank you all.