CSS attributes starting with Hyphens

Heyo,
today I wanted to add some [Custom CSS properties](https://developer.mozilla.org/en-US/docs/Web/CSS/Using_CSS_custom_properties) to my code and noticed that I wasn't able to produce the leading double hyphen, e.g., `--outline-color` with a *camelCased* attribute name. Any Ideas how to get this to work?
I saw mention of auto prefixing certain CSS attributes in the `future-enhancements` section at the bottom of `Hyperscript.jl`. Would this fall into this category?

Cheers