All html files except index.html are generated from similarly named XML files that are maintained in the vscode-xslt-xpath\authoring directory.
To generate the HTML from VS Code, with the XSLT extension installed, you can run the VS Code task labelled createVSCodePages. This runs the very basic XSLT maintained at createPages.xsl
The rationale for generating the HTML with XSLT is so that the header and navigation maintained in index.html can be copied from this file to the HTML files when they are generated from their XML source.