You're looking at StableBuild's Deleted PyPI mirror - where we index all deleted packages from the Python package registry.

jupyterlab-simpledark
0.5.1

This version was deleted from PyPI around 2024-02-04. Installing fails with:
$ pip3 install jupyterlab-simpledark==0.5.1 ERROR: Could not find a version that satisfies the requirement jupyterlab-simpledark==0.5.1
View other deleted versions of jupyterlab-simpledark

Install through StableBuild

You can install this package from StableBuild's PyPI snapshots from before the version was deleted:
pip3 install \ -i https://YOUR_API_KEY.pypimirror.stablebuild.com/2024-02-03/ \ jupyterlab-simpledark==0.5.1
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Or, download files manually

And install manually via pip:
jupyterlab_simpledark-0.5.1-py3-none-any.whl (20.3KB)
jupyterlab-simpledark-0.5.1.tar.gz (486.7KB)