Install and update instructions here apply to plg_system_rca_themer on your Joomla site. The hosted lab at https://recreatinganew.com/themer does not install through Extensions manager; you only need a browser for the lab.
Open System, then Install Extensions, and upload the RCA Themer ZIP from https://recreatinganew.com. Open System, then Plugins, enable System - RCA Themer, and open plugin options. Select Custom CSS file, leave Allow live write off until export works, and leave Beta unlocked on Yes for current free use. Visit the frontend as Super User and confirm the Styles panel appears.
Download the newer Themer ZIP and install it over the existing plugin through System, Install Extensions, or accept the free update feed. Reconfirm Custom CSS file is still selected because upgrades can reset params on some sites. Leave live write off until you re-test export. Clear Joomla cache and open the panel as Super User. Newer 1.1.7 through 1.1.9 builds on the feed may add stylesheet indexing improvements; re-test export after any upgrade.
Export any dirty CSS you still need before uninstall. Open System, Manage, Extensions, and uninstall System - RCA Themer. Your custom.css file and backups under css/_themer_bak/ remain on disk unless you delete them yourself. Remove any leftover HTML kit inject snippets if you ever used that edge path so the panel does not load twice later.
Open https://recreatinganew.com/themer in a modern browser. No Joomla install step exists for the lab. When you export CSS from the lab, paste into your template css/custom.css or the Helix custom CSS field your template documents, then clear Joomla cache on the live site.