rts="partp: part-forwarded1"></custom-element-inner></template>
    <script>installCustomElement("custom-element-outer", "custom-element-outer-template");</script>
    <template id="custom-element-outer-template"><custom-element-middle id="c-e-middle" exportparts="part-forwarded1: part-forwarded2"></custom-element-middle></template>
    The following text should be green:
    <custom-element-outer id="c-e-outer"></custom-element-outer>
    <script>
      "use strict";
      const colorGreen = "rgb(0, 128, 0