Add a styling for :guilabel: inline markup.

demo_docs/source/demo.rst

@@ -106,6 +106,9 @@ RFC reference (:RFC:`2822`); a :sub:`subscript`; a :sup:`superscript`;
 and explicit roles for :emphasis:`standard` :strong:`inline`
 :literal:`markup`.
 
+GUI labels are a useful way to indicate that :guilabel:`Some action` is
+to be taken by the user.
+
 .. DO NOT RE-WRAP THE FOLLOWING PARAGRAPH!
 
 Let's test wrapping and whitespace significance in inline literals:

sass/_theme_rst.sass

@@ -303,6 +303,15 @@
       @extend .fa-download
       &:before
         margin-right: 4px
+  .guilabel
+    border: 1px solid lighten($class-color, 25%)
+    background: lighten($class-color, 50%)
+    font-size: 80%
+    font-weight: 700
+    text-transform: uppercase
+    border-radius: $base-line-height / 6
+    padding: $base-line-height / 6 $base-line-height / 4
+
 
 // Mobile specific
 +media($mobile)