> why not just let them take the (tiny) initial 8kb hit as an external css file, One reason is Google will likely ding your Core Web Vitals score for it, which

> why not just let them take the (tiny) initial 8kb hit as an external css file, One reason is Google will likely ding your Core Web Vitals score for it, which is becoming a ranking signal in May this year (https://developers.google.com/search/blog/2020/11/timing-for-page-experience https://developers.google.com/search/blog/2020/11/timing-for...) so you have less of a choice here for what you prioritise.