Where are things like --appbar-item-height defined?

[Eagle3386]

I've cloned & searched the whole repo, but the only occurrence of the aforementioned variable is this line:

fluentui-blazor/src/Core/Components/AppBar/FluentAppBar.razor.css

Line 4 in a396f75

height: var(--appbar-item-height, 56px);

However, that doesn't only a usage, not a declaration - and the docs neither tell something about where those variables are defined.
I'd like to have a page where all variables, together with their default values, are listed.

Additionally, I'm looking for an explanation why there's a --appbar-item-height, but presumably no --appbar-height - which is what I'm looking for in the first place.
That's because I want to do something like this in my component:

<FluentStack Style="margin-top: calc(50vb - var(--appbar-height) * 1.4); transform: translateY(-50%);">
@* // … left out for brevity… *@
</FluentStack>

If there's some C# DesignTokens.AppBar(.)Height global/static property I can use instead, please let me know as that would be my preferred way!

Can someone help me out?