Labels

Emotion adds a CSS property called label which is appended to the generated class name to make it more readable. @emotion/babel-plugin adds these labels automatically based on the variable name and other information, so they don't need to be manually specified.

// @live
import { css } from '@emotion/react'

let style = css`
  color: hotpink;
  label: some-name;
`

let anotherStyle = css({
  color: 'lightgreen',
  label: 'another-name'
})

let ShowClassName = ({ className }) => (
  <div className={className}>{className}</div>
)

render(
  <div>
    <ShowClassName css={style} />
    <ShowClassName css={anotherStyle} />
  </div>
)

Automatic Labeling at Runtime

If you are not using @emotion/babel-plugin, you can still get automatic labels in development by setting the following global flag:

globalThis.EMOTION_RUNTIME_AUTO_LABEL = true

This feature is opt-in because:

• If you use server-side rendering and test your site in Safari, you may get spurious hydration warnings because the label computed on the server does not match the label computed in Safari.
• This feature may degrade performance if the number of elements using the css prop is very large.