The HTML documentation is not correctly loaded or its behavior is chaotic.
HelpNDoc's responsive HTML 5 template uses advanced techniques to provide a greater user experience and lower download sizes. See: https://www.helpndoc.com/feature-tour/produce-html-websites
Unfortunately, most web-browsers won't allow this code to run on local HTML files (using the file:// protocol) due to security restrictions. That won't happen when the HTML documentation is uploaded to a web server and viewed using the http:// or https:// protocols. And that's why we included a local HTTP web server: HTML documentation can be tested locally as web browsers are tricked into thinking it has been uploaded to a real web server.
The solution is to use HelpNDoc's included HTTP web server or upload the whole documentation file to a real web server.
If browsing local HTML files is mandatory, we recommend the use of the "legacy framed HTML template" that ships with HelpNDoc. Be aware that some web-browsers might block it due to the same security restrictions though. Here is how to select a template for a specific build: https://www.helpndoc.com/step-by-step-guides/how-define-build-settings-helpndoc
HelpNDoc's powerful template system can be used to create completely customized HTML documentation to fit specific requirements. See: Working with templates