revert style changes

[akhmerov]

Closes #452

• I restored the xarray highlight. As a side note, I think a fix on the xarray side would be better: it seems counter-intuitive to require consumers to show elements with [hidden].
• I restored the dd style from basic. This also fixes the autodoc indentation parts. Here, I think we're running into a problem of combining scss for theme asset compilation together with css inheritance. It may be more appropriate to vendor the entire of basic.css into the build chain.
• Restored the white color of the navbar (bootstrap considers that one !important as well).

[akhmerov]

Some of the changes don't seem to come from #451:

Stable:

<dt id="numpy.linalg.eig">
<code class="sig-prename descclassname"><span class="pre">numpy.linalg.</span></code><code class="sig-name descname"><span class="pre">eig</span></code><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">a</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#numpy.linalg.eig" title="Permalink to this definition">¶</a></dt>

Latest:

<dt class="sig sig-object py" id="numpy.linalg.eig">
<span class="sig-prename descclassname"><span class="pre">numpy.linalg.</span></span><span class="sig-name descname"><span class="pre">eig</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">a</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#numpy.linalg.eig" title="Permalink to this definition">¶</a></dt>

Note how the CSS classes are different and even some codes become spans.

I propose to consider this out of scope of the CSS fixes (this PR) and investigate separately—must be something on sphinx side.

[akhmerov]

If this looks OK, I propose to merge as is, and open a separate issue for investigating why the classes and tags of the autodoc changed (it's likely sphinx/autodoc/... version change).

[choldgraf]

Hmm - maybe those are from the latest release of Sphinx. If you downgrade to sphinx 3 do they revert as well?

[choldgraf]

Could you open that issue? I know it wasn't your PR that caused it but I'm on mobile right now!

[akhmerov]

I confirm: the autodoc title looks exactly the same as in stable branch if I downgrade to sphinx 3.5. Not sure how this should be addressed in the theme though.

[akhmerov]

I opened #460

[choldgraf]

LGTM - thanks for following up on this! Merging so that we can get these fixes in

[jorisvandenbossche]

@akhmerov thanks for the quick follow-up here!