Really nice solution, well done!
I only have a few suggestions.
First, the header is a landmark with a banner role. It is meant to hold site-wide content like a logo or nav. It should never contain page specific content like headings because it is for repeating content across a whole site.
Second is to make the card grid have its own container and stick to class names as selectors instead of using element selectors and nth child. Imagine this card grid as a component in a real site. If an author ever wanted to add another bit of content to the page. The styles would break because they're targeting direct children of the main landmark. It's also unnecessarily specific using direct child nth-child in the declarations.
I hope that's helpful. These are more tips about overall architecture but it feels the right time for you to start considering this sort of stuff in the challenges.
Marked as helpful
