Settting display: flex in challenge 2 doesn't work

I’m doing the “Responsive Web Design Certification” / “CSS Flexbox” / Challenge 2.
For some reason even though I’m setting header .follow-btn display’s to flex it keeps showing an error:

Pretty sure this is an error with the challenge since I also tried copying the solution and it still didn’t work.

deactivate the ad-blocker, it’s blocking the follow button in the web preview

Next time, when you have a question about a specific challenge as it relates to your written code for that challenge, just click the Ask for Help button located on the challenge. It will create a new topic with all code you have written and include a link to the challenge also. You will still be able to ask any questions in the post before submitting it to the forum.

Thank you.