Closing your browser will not stop JupyterLab. It will continue to run in the background until it is actively stopped or it reaches its time limit.
To stop your JupyterLab session, you may go to the top bar menu, and then click on File - Hub Control Panel
This will bring you back to your JupyterHub Home, from which you will be able to Stop your server (red button) or connect back to it (blue button)
