CSS, with the layout showing

Forty steps through flexbox, twenty-two builds that fail unless several concepts are right at once, and the famous wtfs underneath — margin collapsing, stacking contexts, and the invisible wall inside every flex item. This is the one subject where the output IS the picture, so every problem is rendered rather than described.

Problems

8 problems in Sizing

All topics Advanced Alignment Distributing space Gap Main axis vs cross axis Making a flex container Order Sizing The famous WTFs The min-width:auto floor Wrapping and the align-content trap

Easy Medium Hard|Teaching step Predict the render Build it Explain the wtf

#	title	topic	type	difficulty
1	flex-grow distributes the surplus, not the container	Sizing	Teaching step	Easy
2	flex-shrink: 0 is defensive CSS	Sizing	Teaching step	Easy
3	The two panels are `flex: 1` and one of them is still wider	Sizing	Build it	Easy
4	The same tiles, keeping the widths the design gave them	Sizing	Build it	Easy
5	Make the three metric tiles exactly equal width	Sizing	Build it	Easy
6	One flexible pane between two fixed rails	Sizing	Build it	Easy
7	Make the documents segment twice the size of the media one	Sizing	Build it	Easy
8	Stop the avatar squashing next to a long name	Sizing	Build it	Easy

44 of 87 catalogue topics are authored, with 37 drills rehearsing them. Every one of them is judged: each carries a starter that has been shown to fail, at least two different correct answers that have been shown to pass, and a set of near-misses and cheats that have been shown to be caught. Nothing reaches this list until all of that holds.