assets directory and mg! macro

[sanity]

I'm trying to understand how the assets/ directory works with the mg! macro, I have this:

const _BULMA_STYLE: &str = manganis::mg!(file("assets/bulma.min.css"));
const _STYLE: &str = manganis::mg!(file("assets/style.css"));

Is this correct? Does it matter what the constants are called? What is pulling these into the page - is it the #[component] macro? Will these be pulled into every page?

I'd appreciate it if someone could point me to an explanation of how this works because it seems a little magical.