Vite released Version 4 at the end of 2022 (which is built on top of Rollup 3). Most of Codex is still using Vite 3, but the Codex Docs are already on Vite 4 since Vitepress (which is still in Alpha) rapidly upgraded to the latest version of Vite.
This inconsistency between Vite versions has come up in the bug at T334222. Vite 4 handles Less syntax in a way that better supports the way our CSS-only icon buttons are styled, so upgrading to use Vite 4 everywhere will solve that particular issue.
However, Vite 3 -> Vite 4 has a number of breaking changes, documented here: https://vitejs.dev/guide/migration.html
The most important one from our perspective is probably the change in the baseline Safari support – Vite 4 drops Safari 13 support.
We should try to complete this upgrade in a timely fashion, but we should also do some QA testing to ensure that there is no adverse impact on users of Codex components.