No affiliation, but I found Dash incredibly helpful for working offline: https://kapeli.com/dash. You can download the docs for most languages/frameworks AND you can download Stackoverflow by section in a way you can read and search.
Unfortunately I am getting "Content rendering error An unhandled error occurred in the application. We apologize for the inconvenience!" for the HTML, CSS and JS references.
edit: That appears to be a bigger issue which has been discussed for some time by a few people (https://github.com/zealdocs/zeal/issues/1155).
find ~/.local/share/Zeal/Zeal/docsets -name "react-main.*.js" -exec rm -rf {} \;
I refresh it before every long haul flight.
* Uses localstorage and sometimes can be cleared.