Container

Composes with the classes `Box` computes instead of replacing them.

The element it paints. `main` or `section` when the container IS the region, so the landmark and the width live on one node instead of two.

Spans the full width, ignoring `size`, while keeping the horizontal padding.

Animates the element in when it first scrolls into view. `true` takes the catalogue entrance; an object tunes it — `preset`, `distance`, `spring`, `duration`, `once`, `amount`, `rootMargin` and `index` for a stagger. It lives here rather than on each surface so that `Card`, `Paper`, `GradientBorder`, `Section` and anything else built on `Box` inherit one implementation. Without it `Box` stays a server component; with it the root swaps for a client shell and the children keep rendering on the server. The entrance is a CSS transition, not a JavaScript animation: it is the only motion in the catalogue that fires WHILE the user scrolls, and the compositor should own it.

Maximum width of the content. The named steps are reading measures, not breakpoints — `xs` 540, `sm` 720, `md` 960, `lg` 1140, `xl` 1320 px — and any other length is taken as written.