Test CSS variable props

[janosh]

Curious if anyone has looked into testing CSS variable props. This doesn't work (even with viteConfig.test.css set to true):

test(`CSS variables are applied`, () => {
  new Component({
    target: document.body,
    props: {
      '--custom-bg-color': `green`,
    },
  })
  const div = document.querySelector(`.some-class`)
  expect(getComputedStyle(div).backgroundColor).toBe(`green`)
})