Programmatic responsiveness: a toolbar that adapts to the room it has - as many tools as fit, whatever their widths, and an ellipsis button that opens the rest in a popover.

• Not something you would typically do with CSS, container queries and breakpoints - ask for it to be designed, and you'll be given a JavaScript solution.
• Nothing is measured anywhere but where it will be: the toolbar puts its tools in the bar one by one, and at the first one that doesn't fit, takes it out again - all before anything is drawn. (Flow had to measure a copy of each tool on its own, off screen.)
• A tool can change width by itself - the size picker, going from 9 to 10: the toolbar notices, and lays out again.