Do pixel densities affect positioning of elements across various devices?

Do pixel densities affect positioning of elements across various devices?

I'm building a custom slideshow and I want my slide controls to always be
at a certain position on the bottom of the window. To accomplish this I'm
using jQuery and setting the top property of the div containing the
controls to the window height - 50px.
My question is, if the site is viewed on a device with a high pixel
density does this approach still work? I have nothing to test on and
appreciate any feedback. In my mind I think that if a device has a high
pixel density 50px will only move it slightly, but I'm hoping I am wrong.