Idea Summary
Flexbox is a powerful concept for designing pages. Although we already have class support (like u-flex), I would say it is challenging to understand what is going on for other developers because you typically don't look for .

I would suggest a region template called flexbox. It has display: flex per default and additional attributes as: 

• justify-content
• flex-direction
• align-items
• flex-wrap
• Some kind of gap / margin between items (see Tailwind for reference)

Conditionally showing attributes on the child region (only when the parent region is of type flexbox) is probably hard, so I am fine with having to add things like  u-flex-grow-1 or u-flex-shrink-1 as classes on the children.

The cherry on top would be if the Page Designer preview could reflect the flexbox attribute. Currently, if you use “Blank with Attributes (No Grid)” and add flex classes, the regions will be previewed in a new row, where in real they stay in the same row.

Use Case
Building rich page designs that don't rely on a grid system.