update app border color
update app border color

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