The **postcss‑flexbox** plugin adds a concise, declarative syntax for building CSS Flexbox layouts using custom `box` and `box-item` properties, which are then converted into standard Flexbox rules (with Autoprefixer handling vendor prefixes). It is aimed at front‑end developers who want an easy‑to‑read way to define horizontal, vertical, and wrapped flex containers and item sizing/alignment without writing verbose Flexbox CSS themselves.