Evaluate need for Startup CSS
Description
Let's use this RFC to reevaluate and discuss the current need for Startup CSS, whether we should keep it (and in what state), or whether we should remove it.
What is Startup CSS?
Startup CSS was introduced in this MR as a means to improve FCP by inlining only the critical CSS needed for the top nav and sidebar of a GitLab page. Our applicaiton.css
is quite large, so being able to just show the critical CSS allows us to defer and parallelize loading the rest of application.css
.
Advantages of Startup CSS
- Improve FCP of a first-visit user
Disadvantages of Startup CSS
- Maintainability cost of duplicating styles. This has been augmented a bit with the recent
startup-css-check
jobs, but managing these jobs is also a cost. - Potentially decreased performance of user with stylesheets already cached.
TODO
We need to verify if the advantages for Startup CSS still outweigh the disadvantages. If not, let's look at removing this.