how to download webgl unity game to use offline

I want to download some game(for using offline and for keep it in archive) which built with Unity in WebGL format. I tried downloading it with wget and HTTrack,but when I running it on local web server I only get errors like this: "An error occurred running Unity content". In Chrome Developer Console I see this: " Failed to load resource: the server responded with a status of 404 (Not Found) UnityLoader.js:3 Invoking error handler due to Script error. index.html:1 Uncaught SyntaxError: Unexpected token < in JSON at position 0 at JSON.parse () at XMLHttpRequest.t.onload (UnityLoader.js:4) index.html:1 Unchecked runtime.lastError: The message port closed before a response was received" Is it possible to download Unity WebGL game? If yes, how? I worried that if this is not possible, that can lead to losing a lot of content,because of sites sometimes went down.