Clean up and add primary selection indicator selector.
Clean up and add primary selection indicator selector.

charnpreetsingh185/jupyterlab,jupyter/jupyterlab,jupyter/jupyterlab,charnpreetsingh185/jupyterlab,charnpreetsingh185/jupyterlab,jupyter/jupyterlab,eskirk/jupyterlab,eskirk/jupyterlab,jupyter/jupyterlab,eskirk/jupyterlab,charnpreetsingh185/jupyterlab,jupyter/jupyterlab,charnpreetsingh185/jupyterlab,eskirk/jupyterlab,eskirk/jupyterlab