Apologies, I went ahead of myself.
I am looking at Gauges because I ultimately want to gain access to the Local SimVars and Events currently inaccessible via SimConnect (for example, from G1000 or A320Neo virtual cockpit).
For now, I am still struggling to get the sample gauge running as you were showing - because I am VS-impaired I could not create "a basic Web project for JS HTML with CSS" in Visual Studio. I can't find a template and, if I do basic .NET Web app, it configures the solution as C# csproj which doesnt help.
From here its all downhill: Debug doesn't work with error "please select a valid startup item", the "set at startup document" context item is not available when I right-click the html file.