Pseudo-elements and animations

A component sheet can style what used to need a hand-written selector — ::before, ::placeholder, @keyframes, transition — with the same typed vocabulary as the rest of the sheet.

Pseudo-elements

import {
  bg,
  blockSize,
  craftStyles,
  cssString,
  defineStateAxis,
  display,
  inlineSize,
  palette,
  pseudo,
  radii,
  radius,
  unit,
  when,
} from '@craft-ts/style';

export const status = defineStateAxis('status', ['failed']);

export const indicator = craftStyles('indicator', {
  root: [
    display.inlineFlex,
    pseudo.before([
      // Without `content`, ::before is never generated — a type error here.
      pseudo.content.empty,
      display.block,
      inlineSize(unit.rem(0.5)),
      blockSize(unit.rem(0.5)),
      radius(radii.full),
      bg(palette.accent.info),
      when(status.failed, [
        pseudo.content.text(cssString('⚠')),
        bg(palette.accent.danger),
      ]),
    ]),
  ],
});

pseudo.before([...]) is an item of a class, and nests like when(...). The emitter always puts the pseudo-element last in the selector, where CSS requires it, whatever the nesting order: when(status.failed, [pseudo.before(...)]) and pseudo.before([when(status.failed, ...)]) both give .x[data-status='failed']::before.

Available: pseudo.before, pseudo.after, pseudo.placeholder, pseudo.marker, pseudo.selection, pseudo.backdrop.

content is required, and typed

::before and ::after are not generated without a content, and nothing they declare applies. Rather than a decoration that silently disappears, it is a type error:

pseudo.before([display.block]);
// ~~~~~~~~~ ERROR_a_generated_pseudo_element_needs_content

The content itself comes from pseudo.content:

helper	CSS
pseudo.content.empty	content: ""
pseudo.content.none	content: none
pseudo.content.text(cssString('→'))	content: "→"
pseudo.content.counter(ident('step'))	content: counter(step)

The check reads the top level of the block: a content placed only under a when(...) leaves the base scenario without one, which is the same bug.

Pseudo-classes are axes

There is no pseudo.hover. :hover, :focus-visible or :disabled are states, and a state is an axis (interaction.hover, defineStateAxis). That is what puts it in the variant contract, the visual matrix and the contrast proof — a hand-written :hover would be invisible to all three.

Keyframes and animations

import { animate, easing, keyframes, rotate } from '@craft-ts/style';

export const spin = keyframes('spin', {
  from: [rotate(unit.deg(0))],
  to: [rotate(unit.deg(360))],
});

export const spinner = craftStyles('spinner', {
  root: [
    ...animate(spin, {
      duration: unit.ms(800),
      easing: easing.linear,
      iterations: 'infinite',
    }),
  ],
});

keyframes(name, steps) returns a token; animate(token, options) plays it. An animation cannot point at keyframes that do not exist. The steps are from, to or percentages, and each step holds declarations from the generated table.

animate writes longhands (animation-name, animation-duration, …), so a variant can change the duration alone. It is not called animation because that name is the generated shorthand helper.

Transitions

import { prop, transitions } from '@craft-ts/style';

export const button = craftStyles('button', {
  root: [
    ...transitions([prop.backgroundColor, prop.color], {
      duration: unit.ms(150),
      easing: easing.easeOut,
    }),
  ],
});

The properties are named from the table (prop.backgroundColor). There is no all: transition: all animates whatever a later variant happens to change, layout included, and nobody decided that.

easing holds the keywords (linear, ease, easeIn, easeOut, easeInOut, stepStart, stepEnd) and two constructors, easing.cubicBezier(x1, y1, x2, y2) and easing.steps(count, position).

Reduced motion

You write none of it. Under prefers-reduced-motion: reduce, the global foundation collapses every animation and transition of the document to an instant.