About the app
This application is both a website and an App. It is called a "Progressive Web App" (PWA). It allows you to save the content for offline use and you can even install the App on your smartphone and make it look like a classic mobile app.
You will have the best compatibility when using an Android phone with Chrome.
IOS supports (less elegantly though) PWAs since version 11.3 using Safari.
How to install on Android + Chrome
When navigating to the website you should see a dialog box inviting you to "Add BGF to Home Screen".
If you don't see it you can select the option manually in your Chrome settings.
How to install on IOS + Safari
When on the website's homepage, clic on the "Share" icon (the square and arrow) and then "on Home Screen".
Unfortunately it is possible the icon does not show up as it should. You may instead see a preview image of the homepage.
You don't have to install the App on your Home Screen to enjoy offline browsing. It just eases the process of accessing the App.
To save the content offline, simply navigate on the pages you are interested in. All the content you see when you are online will be saved on your device.
If you are online you may see the App refreshing by itself. It just means there is a new version online and the new data just got downloaded.