Styling and icons
std/tw writes the theme's utility stylesheet at build time. std/icons turns a pinned icon collection into an import, so a glyph is checked like a name.
Utility classes
std/tw is a generator: it compiles the theme — spacing, color, breakpoints — into one stylesheet at build time. Nothing is fetched at runtime. The whole vocabulary ships, used or not; per-template pruning is a recorded gap, not a feature this page may claim.
Icons
std/icons makes a glyph a name: import { book } from icons("bytesize", "book") generates one function per glyph from a collection pinned in the lock file. A name the collection does not have fails the build. The <Icon> tag draws them.