Date Reference Lines Based on Slicer

Hi, I've looked through the forums around the topic of reference lines but it seems everyone is only concerned with either a specific date (min, max) or today's date. However, I have a date slicer which I would like to create two reference lines on my line graph visual.

So far, I have tried working with the solutions in the forum but the max date is the only result I seem to get. I've tried to hard code a reference line on the graph but I get multiple lines for some reason.

Ideally, I would like to have two reference lines: FIRSTDATE() and LASTDATE() on my slicer. For example, in my slicer I have 2/8 - 2/19 therefore my reference lines should highlight data in that range. (Note: graph drawn in paint app, it's just a rough image of end goal)