insertRule = (container, rule, index) => {
  try {
    if ('insertRule' in container) {
      container.insertRule(rule, index)
    }
    // Keyframes rule.
    else if ('appendRule' in container) {
      container.appendRule(rule)
    }
  } catch (err) {
    warning(false, `[JSS] ${err.message}`)
    return false
  }
  return container.cssRules[index]
}
Read jss nonce setting from the page if the user has set it.