Core Rules

rules: [
  ['m-1', { margin: '0.25rem' }],
  ['font-bold', { 'font-weight': 700 }],
]

rules: [
  // Match m-1, m-2, m-100, etc.
  [/^m-(\d+)$/, ([, d]) => ({ margin: `${d / 4}rem` })],
  
  // Access theme and context
  [/^p-(\d+)$/, (match, ctx) => ({ padding: `${match[1] / 4}rem` })],
]

rules: [
  [/^h-(\d+)dvh$/, ([_, d]) => [
    ['height', `${d}vh`],
    ['height', `${d}dvh`],
  ]],
]

import { symbols } from '@unocss/core'

rules: [
  ['grid', {
    [symbols.parent]: '@supports (display: grid)',
    display: 'grid',
  }],
]

rules: [
  [/^button-(.*)$/, function* ([, color], { symbols }) {
    yield { background: color }
    yield {
      [symbols.selector]: selector => `${selector}:hover`,
      background: `color-mix(in srgb, ${color} 90%, black)`
    }
  }],
]

import { defineConfig, toEscapedSelector as e } from 'unocss'

rules: [
  [/^custom-(.+)$/, ([, name], { rawSelector, theme }) => {
    const selector = e(rawSelector)
    return `
${selector} { font-size: ${theme.fontSize.sm}; }
${selector}::after { content: 'after'; }
@media (min-width: ${theme.breakpoints.sm}) {
  ${selector} { font-size: ${theme.fontSize.lg}; }
}
`
  }],
]

rules: [
  ['custom-red', {
    [symbols.body]: `
      font-size: 1rem;
      &::after { content: 'after'; }
      & > .bar { color: red; }
    `,
    [symbols.selector]: selector => `:is(${selector})`,
  }]
]

<div class="m-2 hover:m2">

.hover\:m2:hover, .m-2 { margin: 0.5rem; }