This is my port of the Material Darker theme for JupyterLab. It's a work in progress.
The extension is not yet uploaded to npm, so in order to install it you need to clone the repository, enter the main directory, and run:
npm run build
jupyter labextension install
(If you get this error in the build process: ERROR in Entry module not found: Error: Can't resolve 'style-loader', run npm install style-loader --save and try building again)
After launching JupyterLab, select the Material Darker theme from the main menu: Settings > JupyterLab Theme > Material Darker
