When creating new Portal sites with the Marquee theme on Xinet 2020.7, you cannot configure the site within the Theme Editor. The same behavior is not seen in Exhibit themed Portal Sites.
The theme editor opens to a blank page without any options showing, as seen below.
This behavior with the Marquee Theme was isolated to a defect within the default portal.css in the 2020.7 release of Xinet.
The Development Team addressed this defect within the Xinet 2021.4 release, and it is recommended that you Upgrade your Xinet Server to 2021.4 or later.