Post navigation previous / next, overlay signs on post image

Hello all,

I’m using self-hosted WordPress installation for my photo blog. To understand my question, please have a quick look here:
https://blogwithphotos.net

As you can see it’s one post = one image rule and I can navigate to previous or next posts by using the buttons prev / next on the top right corner, just above the image.

What I would like is to use something like and overlay symbol / text (like -> or <-) over the image. Rather said, click the right side of the image go previous post, click the left side of the image go next post.
Something like used in this Pixelpost installation: https://www.momentslikethis.de/

I know that this can be done using some js and css map code, but I don know where to start exactly. I did search over Internet, but the return results where not really what I was looking for.

I really appreciate any advice.

Thank you!