Building RTD documentation fails

RTD fails with
 python /home/docs/checkouts/readthedocs.org/user_builds/aisim/envs/fix_docs/bin/sphinx-build -T -b readthedocs -d _build/doctrees-readthedocs -D language=en . _build/html
Running Sphinx v1.8.5
loading translations [en]... done

Traceback (most recent call last):
  File "/home/docs/checkouts/readthedocs.org/user_builds/aisim/envs/fix_docs/lib/python3.7/site-packages/sphinx/cmd/build.py", line 303, in build_main
    args.tags, args.verbosity, args.jobs, args.keep_going)
  File "/home/docs/checkouts/readthedocs.org/user_builds/aisim/envs/fix_docs/lib/python3.7/site-packages/sphinx/application.py", line 228, in __init__
    self.setup_extension(extension)
  File "/home/docs/checkouts/readthedocs.org/user_builds/aisim/envs/fix_docs/lib/python3.7/site-packages/sphinx/application.py", line 449, in setup_extension
    self.registry.load_extension(self, extname)
  File "/home/docs/checkouts/readthedocs.org/user_builds/aisim/envs/fix_docs/lib/python3.7/site-packages/sphinx/registry.py", line 472, in load_extension
    mod = __import__(extname, None, None, ['setup'])
  File "/home/docs/checkouts/readthedocs.org/user_builds/aisim/envs/fix_docs/lib/python3.7/site-packages/nbsphinx.py", line 41, in <module>
    import nbconvert
  File "/home/docs/checkouts/readthedocs.org/user_builds/aisim/envs/fix_docs/lib/python3.7/site-packages/nbconvert/__init__.py", line 4, in <module>
    from .exporters import *
  File "/home/docs/checkouts/readthedocs.org/user_builds/aisim/envs/fix_docs/lib/python3.7/site-packages/nbconvert/exporters/__init__.py", line 4, in <module>
    from .slides import SlidesExporter
  File "/home/docs/checkouts/readthedocs.org/user_builds/aisim/envs/fix_docs/lib/python3.7/site-packages/nbconvert/exporters/slides.py", line 12, in <module>
    from ..preprocessors.base import Preprocessor
  File "/home/docs/checkouts/readthedocs.org/user_builds/aisim/envs/fix_docs/lib/python3.7/site-packages/nbconvert/preprocessors/__init__.py", line 7, in <module>
    from .csshtmlheader import CSSHTMLHeaderPreprocessor
  File "/home/docs/checkouts/readthedocs.org/user_builds/aisim/envs/fix_docs/lib/python3.7/site-packages/nbconvert/preprocessors/csshtmlheader.py", line 14, in <module>
    from jupyterlab_pygments import JupyterStyle
  File "/home/docs/checkouts/readthedocs.org/user_builds/aisim/envs/fix_docs/lib/python3.7/site-packages/jupyterlab_pygments/__init__.py", line 4, in <module>
    from .style import JupyterStyle
  File "/home/docs/checkouts/readthedocs.org/user_builds/aisim/envs/fix_docs/lib/python3.7/site-packages/jupyterlab_pygments/style.py", line 10, in <module>
    class JupyterStyle(Style):
  File "/home/docs/checkouts/readthedocs.org/user_builds/aisim/envs/fix_docs/lib/python3.7/site-packages/pygments/style.py", line 101, in __new__
    ndef[0] = colorformat(styledef)
  File "/home/docs/checkouts/readthedocs.org/user_builds/aisim/envs/fix_docs/lib/python3.7/site-packages/pygments/style.py", line 58, in colorformat
    assert False, "wrong color format %r" % text
AssertionError: wrong color format 'var(--jp-mirror-editor-variable-color)'

Exception occurred:
  File "/home/docs/checkouts/readthedocs.org/user_builds/aisim/envs/fix_docs/lib/python3.7/site-packages/pygments/style.py", line 58, in colorformat
    assert False, "wrong color format %r" % text
AssertionError: wrong color format 'var(--jp-mirror-editor-variable-color)'
The full traceback has been saved in /tmp/sphinx-err-_xoeql76.log, if you want to report the issue to the developers.
Please also report this if it was a user error, so that a better error message can be provided next time.
A bug report can be filed in the tracker at <https://github.com/sphinx-doc/sphinx/issues>. Thanks!
bleykauf / aisim

Building RTD documentation fails #58
