#CSS breakpoints: I haven’t found any good sources that explain the “break” part of that term. Maybe: That’s the point at which the layout breaks? All material on responsive design I have seen explains what a breakpoint is but not why that term was chosen. Traditionally, it meant something very different:

Breakpoint - Wikipedia

#CSS—this doesn’t seem to be possible: @​container (width < var(--width-break)) and (height >= var(--height-break)) { … }

#CSS: flexbox diagram with the most important terms