Your Mac may be temporarily disconnected from the Internet because you moved it somewhere that doesn’t have a Wi-Fi network, or the Wi-Fi network isn’t working. Try again when your Mac is in a location that you know has a working Wi-Fi network.
Your Internet connection might be out of order due to a malfunctioning router or modem, or your Internet service provider (ISP) might be experiencing an outage. To solve Internet connection problems, use Network Diagnostics.
While you’re offline, you can read articles that you already added to your Reading List. To show it, click the Sidebar button
in the toolbar, then click the Reading List button 
at the top of the sidebar.