Setting a Background for the complete Presentation/Markdown file

[v-scalone]

I am just writing my first presentation and I have the following problem: I want to set a background image for my whole presentation.
I found out that I could set it per slide with

<!-- .slide: data-background="./bg.png", data-background-size="contain" -->

but it makes the markdown file really cluttered >.<

I couldn't find a way to just have something like

data-background: ./bg.png
data-background-size: contain

in the upfront yaml configuration

[webpro]

This is the way to it indeed. You can search this repo, I've seen this being discussed a few times before, maybe you'll find an alternative you like better.