Css file doesn't work off server: Firefox might be giving me a clue
Briefly

When serving web pages from an ESP32 web socket server, CSS and JavaScript files may not load properly due to MIME type issues. The browser detects these files as 'text/html' instead of their intended types. This is often a result of incorrect server configuration in specifying MIME types. The solution involves setting the correct MIME types for the CSS and JS files so that the browser can interpret them correctly and apply the styles and scripts as intended.
The MIME type of the served CSS and JS files from the ESP32 is detected as 'text/html', causing browsers to ignore these styles and scripts.
Read at SitePoint Forums | Web Development & Design Community
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