title: Fix some very minor issues and rebuild sphinx but got the error "wrong color format"
body: <p>I had some minimal updates in the &quot;source&quot; folder and rebuilt the HTML using <code>make html</code> command. Everything works fine and I synced the folder to GitHub. However, when I was rebuilding the doc on the Read the Docs website, I got an error like this right after <code>cat source/conf.py</code> :</p>
  <pre><code>AssertionError: wrong color format 'var(--jp-mirror-editor-variable-color)'
  </code></pre>
  <p>I just added some texts and fixed some typos in my documentation, nothing more. Why this error occurred and the build failed? Thanks.</p>
  <pre class="lang-none prettyprint-override"><code>Traceback (most recent call last):
    File &quot;/home/docs/checkouts/readthedocs.org/user_builds/pkg_name/envs/latest/lib/python3.7/site-packages/sphinx/cmd/build.py&quot;, line 303, in build_main
      args.tags, args.verbosity, args.jobs, args.keep_going)
    File &quot;/home/docs/checkouts/readthedocs.org/user_builds/pkg_name/envs/latest/lib/python3.7/site-packages/sphinx/application.py&quot;, line 228, in __init__
      self.setup_extension(extension)
    File &quot;/home/docs/checkouts/readthedocs.org/user_builds/pkg_name/envs/latest/lib/python3.7/site-packages/sphinx/application.py&quot;, line 449, in setup_extension
      self.registry.load_extension(self, extname)
    File &quot;/home/docs/checkouts/readthedocs.org/user_builds/pkg_name/envs/latest/lib/python3.7/site-packages/sphinx/registry.py&quot;, line 472, in load_extension
      mod = __import__(extname, None, None, ['setup'])
    File &quot;/home/docs/checkouts/readthedocs.org/user_builds/pkg_name/envs/latest/lib/python3.7/site-packages/nbsphinx.py&quot;, line 41, in &lt;module&gt;
      import nbconvert
    File &quot;/home/docs/checkouts/readthedocs.org/user_builds/pkg_name/envs/latest/lib/python3.7/site-packages/nbconvert/__init__.py&quot;, line 4, in &lt;module&gt;
      from .exporters import *
    File &quot;/home/docs/checkouts/readthedocs.org/user_builds/pkg_name/envs/latest/lib/python3.7/site-packages/nbconvert/exporters/__init__.py&quot;, line 4, in &lt;module&gt;
      from .slides import SlidesExporter
    File &quot;/home/docs/checkouts/readthedocs.org/user_builds/pkg_name/envs/latest/lib/python3.7/site-packages/nbconvert/exporters/slides.py&quot;, line 12, in &lt;module&gt;
      from ..preprocessors.base import Preprocessor
    File &quot;/home/docs/checkouts/readthedocs.org/user_builds/pkg_name/envs/latest/lib/python3.7/site-packages/nbconvert/preprocessors/__init__.py&quot;, line 7, in &lt;module&gt;
      from .csshtmlheader import CSSHTMLHeaderPreprocessor
    File &quot;/home/docs/checkouts/readthedocs.org/user_builds/pkg_name/envs/latest/lib/python3.7/site-packages/nbconvert/preprocessors/csshtmlheader.py&quot;, line 14, in &lt;module&gt;
      from jupyterlab_pygments import JupyterStyle
    File &quot;/home/docs/checkouts/readthedocs.org/user_builds/pkg_name/envs/latest/lib/python3.7/site-packages/jupyterlab_pygments/__init__.py&quot;, line 4, in &lt;module&gt;
      from .style import JupyterStyle
    File &quot;/home/docs/checkouts/readthedocs.org/user_builds/pkg_name/envs/latest/lib/python3.7/site-packages/jupyterlab_pygments/style.py&quot;, line 10, in &lt;module&gt;
      class JupyterStyle(Style):
    File &quot;/home/docs/checkouts/readthedocs.org/user_builds/pkg_name/envs/latest/lib/python3.7/site-packages/pygments/style.py&quot;, line 101, in __new__
      ndef[0] = colorformat(styledef)
    File &quot;/home/docs/checkouts/readthedocs.org/user_builds/pkg_name/envs/latest/lib/python3.7/site-packages/pygments/style.py&quot;, line 58, in colorformat
      assert False, &quot;wrong color format %r&quot; % text
  AssertionError: wrong color format 'var(--jp-mirror-editor-variable-color)'
  
  Exception occurred:
    File &quot;/home/docs/checkouts/readthedocs.org/user_builds/pkg_name/envs/latest/lib/python3.7/site-packages/pygments/style.py&quot;, line 58, in colorformat
      assert False, &quot;wrong color format %r&quot; % text
  AssertionError: wrong color format 'var(--jp-mirror-editor-variable-color)'
  The full traceback has been saved in /tmp/sphinx-err-scp_kb7h.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 &lt;https://github.com/sphinx-doc/sphinx/issues&gt;. Thanks!
  </code></pre>