How do I add CSS styling to my header menu?

Can someone help with how I can add css styling to my header navigation, I’d like to add the following css style: mix-blend-mode: exclusion

I’m only seeing js code panel, which I have no experience in.

Hi,

Im Ido from the Editor X team,
You can not add css styling to Editor elements.
I will pass on your request to our Product teams feature request to add blend modes to elements.

Thanks ,

Ido.