Block formatting context

An independent layout region whose contents cannot interact with the layout outside it: floats are contained, margins do not collapse through it, and it does not overlap adjacent floats. It is created by side effects of other properties — `overflow` other than visible, `display: flow-root`, flex and grid containers, absolute positioning — which is why the fixes for float and margin bugs have always looked like unrelated magic. `display: flow-root` exists to create one on purpose, with no side effects.