Align First-Contribution tutorial with click-through demo

What does this MR do and why?

In the click through demo (https://gitlab.navattic.com/ak10d67) we're targeting the line "Customize the color of GitLab". I'm aware that we've changed this in !139475 (merged) (Thanks @davidwatts111) but now it is out of sync and added a bit of complexity to the tutorial as it is not in line with the Click-Through demo.

I've modified both the click-through demo and the tutorial (with this MR) so they are aligned. We should also not explain historical changes in the tutorial as that only causes more confusion I believe.