Revert "docs: use pmOS green color in html output (MR 66)"

This was merged without maintainer approval and is not a trivial fix, so
it is a violation of our rules for merging. Additionally, I do not agree
with these changes in their current form, see [1] for my reasoning.

This reverts commit da492e4a.

 [1]: pmbootstrap#2534

docs/_static/pmOS.css

-/* pmOS styling color */
-body {
-  --themecolor: #009900;
-}
-
-/* sets the menu bg color for desktop layout */
-.wy-side-nav-search {
-  background-color: var(--themecolor)
-}
-/* sets the menu bg color for mobile layout */
-.wy-nav-top {
-  background-color: var(--themecolor)
-}

docs/conf.py

@@ -58,11 +58,6 @@ html_theme_options = {
     "style_external_links": True,
 }
 
-# customize styling
-html_static_path = ["_static"]
-html_css_files = ["pmOS.css"]
-
-
 # -- Options for manual page output ---------------------------------------
 
 # One entry per manual page. List of tuples