At first the title made me think of Git conflicts, but that's not what this is about. It's about namespacing selectors for components. Ultimately, they decided to use a Webpack loader (not open source, it doesn't appear) to prefix every single class with a hashed string representing the version. I guess that must happen in both the HTML and CSS so they match. Lots of folks landing on style-scoping in one way or another to solve their problems.
It makes me think about another smaller-in-scope issue. Say you have an alternate version of a header that you're going to send to 5% of your users. It has different HTML and CSS. Easy enough to send different HTML to users from the server. But CSS tends to be bundled, and it seems slightly impractical to make an entirely different CSS bundle for a handful of lines of CSS. One solution: add an additional attribute to the new header and ship the new CSS with artificially-boosted specificity to avoid all the old CSS. Then when you go live, remove the new attribute from both.