doc-rst: add CSS styles for :kbd: and :menuselection:

As we're about to use those two markups, add them to the
theme style overrride.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/sphinx-static/theme_overrides.css

@@ -42,6 +42,20 @@
     caption a.headerlink { opacity: 0; }
     caption a.headerlink:hover { opacity: 1; }
 
+    /* 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
+    }
+
     /* inline literal: drop the borderbox and red color */
 
     code, .rst-content tt, .rst-content code {
@@ -54,5 +68,4 @@
     .rst-content tt.literal,.rst-content tt.literal,.rst-content code.literal {
         color: inherit;
     }
-
 }