docs: add support for RTD dark mode

This is actually an overlay on the top of the RTD theme, which
requires to include first the RTD theme.

It should be noticed that, when the dark theme is used, the
DOCS_CSS files won't be the last CSS themes. So, it won't
override the dark.css style by default. So, it is needed
to force the them override with "!important".

This small script, for instance, produces a nice output with
the RTD dark theme:

	DOCS_THEME=sphinx_rtd_dark_mode
	cat << EOF > dark_override.css
	  html body {
	    font-family: arial,helvetica,sans-serif;
	  }
	  html[data-theme='dark'] body {
	    color: white !important;
	  }
	  html[data-theme='dark'] .sig-name {
	    color: green !important;
	  }
	  html[data-theme='dark'] .wy-menu-vertical a {
	    color: #ffcc00 !important;
	  }
	  html[data-theme="dark"] h1, html[data-theme="dark"] h2, html[data-theme="dark"] h3 {
	    color: #ffcc00 !important;
	  }
	  html[data-theme="dark"] h4, html[data-theme="dark"] h5, html[data-theme="dark"] h6 {
	    color: #ffcc00 !important;
	  }
	  html[data-theme="dark"] h7, html[data-theme="dark"] h8, html[data-theme="dark"] h9 {
	    color: #ffcc00 !important;
	  }
	  html[data-theme="dark"] .wy-nav-content a, html[data-theme="dark"] .wy-nav-content a:visited {
	    color: #ffcc00 !important;
	  }
	EOF

	make DOCS_CSS=dark_override.css DOCS_THEME=sphinx_rtd_dark_mode htmldocs

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/90d316e055ef7f4c9021b9eada8f8d3b2e750a66.1638870323.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/conf.py

@@ -215,7 +215,7 @@
 if "DOCS_THEME" in os.environ:
     html_theme = os.environ["DOCS_THEME"]
 
-if html_theme == 'sphinx_rtd_theme':
+if html_theme == 'sphinx_rtd_theme' or html_theme == 'sphinx_rtd_dark_mode':
     # Read the Docs theme
     try:
         import sphinx_rtd_theme
@@ -227,6 +227,19 @@
         html_css_files = [
             'theme_overrides.css',
         ]
+
+        # Read the Docs dark mode override theme
+        if html_theme == 'sphinx_rtd_dark_mode':
+            try:
+                import sphinx_rtd_dark_mode
+                extensions.append('sphinx_rtd_dark_mode')
+            except ImportError:
+                html_theme == 'sphinx_rtd_theme'
+
+        if html_theme == 'sphinx_rtd_theme':
+                # Add color-specific RTD normal mode
+                html_css_files.append('theme_rtd_colors.css')
+
     except ImportError:
         html_theme = 'classic'
 

Documentation/sphinx-static/theme_overrides.css

@@ -1,32 +1,23 @@
 /* -*- coding: utf-8; mode: css -*-
  *
  * Sphinx HTML theme customization: read the doc
- *
+ * Please don't add any color definition here, as the theme should
+ * work for both normal and dark modes.
  */
 
 /* Improve contrast and increase size for easier reading. */
 
 body {
 	font-family: serif;
-	color: black;
 	font-size: 100%;
 }
 
 h1, h2, .rst-content .toctree-wrapper p.caption, h3, h4, h5, h6, legend {
 	font-family: sans-serif;
 }
 
-.wy-menu-vertical li.current a {
-	color: #505050;
-}
-
-.wy-menu-vertical li.on a, .wy-menu-vertical li.current > a {
-	color: #303030;
-}
-
 div[class^="highlight"] pre {
 	font-family: monospace;
-	color: black;
 	font-size: 100%;
 }
 
@@ -104,13 +95,10 @@ div[class^="highlight"] pre {
     /* Menu selection and keystrokes */
 
     span.menuselection {
-	color: blue;
 	font-family: "Courier New", Courier, monospace
     }
 
     code.kbd, code.kbd span {
-	color: white;
-	background-color: darkblue;
 	font-weight: bold;
 	font-family: "Courier New", Courier, monospace
     }

Documentation/sphinx-static/theme_rtd_colors.css

@@ -0,0 +1,37 @@
+/* -*- coding: utf-8; mode: css -*-
+ *
+ * Sphinx HTML theme customization: color settings for RTD (non-dark) theme
+ *
+ */
+
+/* Improve contrast and increase size for easier reading. */
+
+body {
+	color: black;
+}
+
+.wy-menu-vertical li.current a {
+	color: #505050;
+}
+
+.wy-menu-vertical li.on a, .wy-menu-vertical li.current > a {
+	color: #303030;
+}
+
+div[class^="highlight"] pre {
+	color: black;
+}
+
+@media screen {
+
+    /* Menu selection and keystrokes */
+
+    span.menuselection {
+	color: blue;
+    }
+
+    code.kbd, code.kbd span {
+	color: white;
+	background-color: darkblue;
+    }
+}