Can I use eleventyComputed to output aggregate data from rendering other files?

[mbforbes]

Hello!

While rendering pages, I am using shortcodes to accumulate CSS classes I'd like to generate. I'm hoping to then dump them all in a .css file at the end of the build.

From reading the docs, it seems like eleventyComputed could do this. I am able to generate a .css file that spits out a value from eleventyComputed. My problem is this value is determined at the beginning of eleventy's build, not at the end. I need to write out all my pages (which call the shortcodes that generate the CSS classes), and then at the end, spit out the CSS.

In case it helps, the build order looks like this:

Setting myGeneratedCSS in .eleventy.js
Getting generatedCSS (eleventyComputed) now.
[11ty] Writing _site/404.html from ./404.njk
[11ty] Writing _site/posts/2022-manila/index.html from ./posts/writing/travel/2022-manila.md (njk)
[11ty] Writing _site/posts/2022-penang/index.html from ./posts/writing/travel/2022-penang.md (njk)
[11ty] Writing _site/posts/2022-seoul/index.html from ./posts/writing/travel/2022-seoul.md (njk)
...

I need the second step (Getting generatedCSS (eleventyComputed) now.) to happen at the end of the build, because the value is modified throughout the build process.

This might be impossible using eleventyComputed. If so, I would love a suggestion for how to accomplish my task in Eleventy!

Apologies if this is unclear, I'm happy to provide more details or another shot at the description if that'd be helpful.