Utilities/Sphinx: Make HTML links in parsed-literal blocks more obvious

Hyperlink text color does not stand out when used inside a literal block
because such blocks typically get syntax highlighting.  Update our CSS
style to make the links more distinct.

Suggested-by: Kyle Edwards <kyle.edwards@kitware.com>

Utilities/Sphinx/static/cmake.css

@@ -6,3 +6,13 @@
 div.sphinxsidebarwrapper {
   word-wrap: break-word;
 }
+
+/* Make links inside parsed-literal blocks more obvious
+   by using a background color and increased line spacing
+   to make them look boxed.  */
+.literal-block {
+  line-height: 1.4;
+}
+.literal-block a.reference.internal {
+  background-color: #dfdfdf;
+}