docs: Inherit some more background colors

Unfortunately sphinx hardcodes these again in classic.css, and if we
want to change them we need to make these the same again.

doc_src/python_docs_theme/static/pydoctheme.css

@@ -27,6 +27,7 @@ div.related {
     padding: 0.5em 0;
     border-top: 1px solid #ccc;
     margin-top: 0;
+    background-color: inherit;
 }
 
 div.section {
@@ -91,6 +92,11 @@ div.documentwrapper {
     float: none;
 }
 
+div.document, div.body {
+    background-color: inherit;
+    color: inherit;
+}
+
 div#searchbox {
     /* Cheesy: The padding is on the sphinxsidebar*wrapper*,
        so if this is the last element the bottom padding won't apply.
@@ -250,7 +256,7 @@ div.footer a:hover {
 }
 
 .highlight {
-    background: #FFF !important;
+    background: #FFF;
 }
 
 dl > dt span ~ em {