code: function toRules (cssText) {
    const node = parseCss(cssText)
    let rules = []
  
    if (node.rules && node.rules.length > 0) {
      rules = node.rules
        .filter(filterUnusedVendorRule)
        .map((rule) => toCssText(rule))
    } else {
      const cssText = toCssText(node)
      if (cssText) {
        rules = [cssText]
      }
    }
  
    return rules
  }
docs: Parses a string of CSS into an array of rules objects (selector + declaration block)
  Filters out any vendor rules that don't apply to the current browser
  @param {String} CSS text to parse
  @returns {Array} an array of rules objects