Flexbox doesn’t have anything to do with Kirby itself. Kirby is the CMS (PHP) and we as developers can define the templates for it. Flexbox is CSS and not all browsers do support it (without vendor prefixes).
Something in that manner. I assume you’re going to customize it to fit your needs and going to add the necessary prefiexes yourself or via Autoprefixer.
You also need to define properties for the article element itself, otherwise it’s recognized as a block-level element, and will take up the full width of its container (you’re naming this “.row”). In your example, .fluid and “article” are both assumed to be block elements. In your JSbin, can you please toss in your code for .fluid and <article> as well? It’s impossible to see what else could be wrong without having all the necessary code to look at. Also, I think on lines 75 + 76, your “endforeach” and “endif” statements are out of place. At the very least, the “endif” statement is incorrectly placed (I believe it should be directly after </article>).