From a technical perspective a standard web page could be saved in single HTML file that can be opened offline (with all JS/CSS inlined and images base64 encoded and inclined)--so it can be as easy as double-clicking on a file (just an .html file instead of .ppt).
The average user probably lacks this knowledge though and wouldn't know to or try to double-click on an html file but it is technically feasible.
Microsoft had technology to do just this in 1999 (!). It was known as 'HTA' (Html Applications) but was ahead of its time - the rich DOM manipulation and CSS effects we have now didn't exist. HTA was discontinued years ago afaik, but in hindsight it was a peak at the future.
The average user probably lacks this knowledge though and wouldn't know to or try to double-click on an html file but it is technically feasible.