Frontend & browser·Layout, CSS and the cascade
you defined the columns once on the container and the children fell into place without any width of their own.
CSS grid
Also calledgrid layout, display: grid
A two-dimensional layout model where the container defines rows and columns and items are placed into them. It is the right tool whenever alignment must hold across both axes, which flexbox cannot guarantee because each of its lines is sized independently. The trade is that the structure lives on the parent, so a component cannot fully control its own placement without the parent cooperating — which is exactly what `subgrid` addresses.