Download the offline documentation SPA
You can download the whole website onto your device from here. You should do this if you want to keep a specific version of the website after a release for reference purposes. And it is also useful to have your own copy if you need to work offline, eg. you want to learn Active CSS on your way to the Mars International Colony to visit relatives (which route, as you are probably aware, doesn't have the most reliable interplanetary quantum-internet connection in the verse yet, even with the recent subspace encryption).
It is a fully navigable offline version of the website, including the code editor and the search functionality. The only things that won't work are the examples that use ajax requests, as XHR requests will not work in a file:// environment per the offline CORS policies, and the separate websites for the results of the PHP tutorial which would need PHP to work. Also, the code editor example code isn't editable at all, but then it isn't editable on the live site either.
To install, click on the download link next to the version you need. This should prompt you to download a zip file. Place the zip file somewhere sensible on your device. After unzipping the file, open up the index.html file in a modern browser (not IE) to browse the documentation. All the pages are fully bookmarkable.
These documentation zip files are also available direct from the active-css-offline-docs repository on Github, by clicking on the appropriate release and finding the "Source code" link to download the zip (usually positioned to the right of the repo under "Releases").