core(unused-css): change title Defer -> Remove

[patrickhulce]

Summary
It's a bit confusing that the unused CSS is probably dead CSS that's completely unused. We'll save that distinction for the help text and make the title a little more aggressive.

Related Issues/PRs
closes #6588

[exterkamp]

LGTM, I +1 this new language, it is a lot more direct what's going on and what we're looking for.

[cagross]

This is good news--thank you. This should help clear up the the defer vs. remove issue.

But what about the remaining ambiguity on the Learn More page? Specifically, the title refers to 'unused CSS.' But the Learn More page describes 'critical CSS' and 'uncritical CSS.' I was under the impression all three were separate:

Critical CSS: CSS rules used on the page that affect above-the-fold content, which, if removed, could result in noticeable differences in layout/style.

Uncritical CSS: CSS rules used on the page that affect below-the-fold content, or content not viewable on immediate page load (e.g. in a modal window that the user might open on the page)/

Unused CSS: CSS rules that have no chance at all of being used on the page.

If we use these three designations, it sounds like the optimum way to deal with all would be to inline critical CSS, defer uncritical CSS, and remove unused CSS. Is this indeed how PageSpeed Insights suggests we do things? If so, I don't think the "Learn More" page makes that very clear. Or am I misunderstanding the way in which PageSpeed Insights suggests we load the three types of CSS?

Also, maybe this isn't the place to bring this up? If you'd like me to create a new issue, or append it to an existing issue, I can do that.

[patrickhulce]

You are right @cagross that is the breakdown of the 3 categories of CSS we're recommending. The documentation is currently managed over in another repo which moves a little slower than core. That's where a fix would be done for that issue.

[cagross]

@patrickhulce OK thanks for confirming that there are three distinct CSS 'types,' and what I described corresponds to Google's suggested treatment for each. But where would I suggest that the verbiage of the Learn More page be modified to reflect this? Are you saying I should bring that up as in issue in the WebFundamentals repo? Or are you perhaps saying that the WebFundamentals repo needs to first approve this as best practice, then the Lighthouse repo needs to modify the text on the Learn More page accordingly? Or something else? Or is this already in the works, and I need not concern myself too much with it?

[patrickhulce]

The change itself will take place in that other repo. It's in the backlog to update, but I'll go ahead and re-open the issue this closed to track its progress.

No further action from you necessary :)

[cagross]

@patrickhulce OK got it, sounds good. I see that you re-opened the other ticket. I'll monitor progress there. Thanks very much for confirming everything and giving helpful info.