docs: add a number of CSS fixes (#2078)

Fix a number of issues related to the vertical alignment and margins of
list elements.

docs/_static/css/custom.css

+/*
+  This fixes the vertical position of list markers when the first
+  element in the <li> is a <pre> block
+
+  Scrolling inside the <pre> block is still working as expected
+*/
+.rst-content pre.literal-block,
+.rst-content div[class^='highlight'] pre {
+	overflow: visible;
+}
+
+
+/*
+  This fixes the bottom margin of paragraphs inside lists, where margins inside
+  a single list item would incorrectly be displayed larger than margins between
+  the list items.
+
+  Upstream fix (not fixed on readthedocs.io yet):
+  https://github.com/readthedocs/sphinx_rtd_theme/commit/ac20ce75d426efeb40fe2af1f89ea9bad285a45b
+*/
+.rst-content .section ol li > p,
+.rst-content .section ol li > p:last-child,
+.rst-content .section ul li > p,
+.rst-content .section ul li > p:last-child {
+	margin-bottom: 12px;
+}
+.rst-content .section ol li > p:only-child,
+.rst-content .section ol li > p:only-child:last-child,
+.rst-content .section ul li > p:only-child,
+.rst-content .section ul li > p:only-child:last-child {
+	margin-bottom: 0rem;
+}
+
+/*
+  This fixes the bottom margin of nested lists
+
+  Based on upstream fix (not on readthedocs.io yet):
+  https://github.com/readthedocs/sphinx_rtd_theme/commit/6f0de13baff93f25204aa2cdf0308aae47d71312
+*/
+.rst-content .section ul li > ul,
+.rst-content .section ul li > ol,
+.rst-content .section ol li > ul,
+.rst-content .section ol li > ol {
+	margin-bottom: 12px;
+}

docs/conf.py

@@ -89,7 +89,7 @@ html_theme = 'sphinx_rtd_theme'
 # relative to this directory. They are copied after the builtin static files,
 # so a file named "default.css" will overwrite the builtin "default.css".
 #
-# html_static_path = ['_static']
+html_static_path = ['_static']
 
 # Custom sidebar templates, must be a dictionary that maps document names
 # to template names.
@@ -101,6 +101,10 @@ html_theme = 'sphinx_rtd_theme'
 #
 # html_sidebars = {}
 
+# These paths are either relative to html_static_path
+# or fully qualified paths (eg. https://...)
+html_css_files = ['css/custom.css']
+
 
 # -- Options for HTMLHelp output ---------------------------------------------