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>

1 files changed, 37 insertions, 0 deletions

diff --git a/Documentation/sphinx-static/theme_rtd_colors.css b/Documentation/sphinx-static/theme_rtd_colors.css
new file mode 100644
index 000000000000..55b6e1c3664b
--- /dev/null
+++ b/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;
+    }
+}