plumber-sass | Easy baseline grid with SASS | Style Language library

EDIT: I've simplified the code (below and in fiddle) down to the major problem needed to be solved in hope of creating more readability.

I've implemented Bader's solution for correctly using getBoundingClientRect value and using document.querySelector for getting both the class name and the html tag needed for the function. I'd now like to move on to the last five lines of the code beginning with var = style.

I've now corrected the math for the final two variables.

→ I'm trying to achieve creating a snapping function for use alongside Plumber, a baseline-grid Sass plugin.

Basically, I have a vertically centered flex item that needs to -- instead of being perfectly centered -- snap in an upward direction to the closest grid line. This will allow me to have a consistent vertical rhythm between slides in a custom mobile-based experience.

I'm using getBoundingClientRect to calculate the distance between the bottom of an object, and the top of the window.

Then I use Math.floor to round down to the nearest multiple of my rem value.

Then I use this new value to create a CSS bottom margin on the flex-centered container for the alignment fix.

(Then to finish, I'd like to have this function load on $(document).ready and on window resize.)