How Do I Activate Full Screen Mode When Playing a Game?

At the bottom of the game play screen, you can find the following buttons:

From the left to the right:

1. Focus mode: darken the background so that you can focus more on your game
2. Favourite button: add your the game as your favourite
3. Full-screen button: this is to play the game in full screen. This is also useful to play certain games on mobile devices such as Bitlife Simulator.
4. Flag button: to report an issue with the game
5. Share button: to share the game to your social media