function computeSelector(id, css) {
  const selectoPlaceholderRegexp = /__jsx-style-dynamic-selector/g
  // Sanitize SSR-ed CSS.
  // Client side code doesn't need to be sanitized since we use
  // document.createTextNode (dev) and the CSSOM api sheet.insertRule (prod).
  if (typeof window === 'undefined') {
    css = sanitize(css)
  }

  const idcss = id + css
  if (!cache[idcss]) {
    cache[idcss] = css.replace(selectoPlaceholderRegexp, id)
  }

  return cache[idcss]
}
computeSelector

Compute and memoize dynamic selectors.