resolves asciidoctor#451 which suggest to use a stylable background f…

…or btn:

Currently just a test commit to trigger feedback how to set the background colof a text element

data/themes/default-theme.yml

@@ -71,6 +71,8 @@ literal:
   font_color: b12146
   font_family: M+ 1mn
 menu_caret_content: " <font size=\"1.15em\"><color rgb=\"b12146\">\u203a</color></font> "
+button:
+  background_color: e7e7e7
 heading:
   #font_color: 181818
   font_color: $base_font_color

lib/asciidoctor-pdf/converter.rb

@@ -1406,8 +1406,16 @@ def convert_inline_break node
     %(#{node.text}<br>)
   end
 
-  def convert_inline_button node
-    %(<strong>[#{NarrowNoBreakSpace}#{node.text}#{NarrowNoBreakSpace}]</strong>)
+ def convert_inline_button node
+    button_bg_color = resolve_theme_color :button_background_color
+    if (button_bg_color)
+      # TODO use the button_bg_color to set the background of the node.text. Maybe similar to the following?
+      #%( <background-color> rgb=#{button_bg_color}><strong>[#{node.text}]</color></background-color>)
+      # Remove the following line once the TODO is fixed
+      %(<strong>[#{NarrowNoBreakSpace}#{node.text}#{NarrowNoBreakSpace}]</strong>)
+    else
+      %(<strong>[#{NarrowNoBreakSpace}#{node.text}#{NarrowNoBreakSpace}]</strong>)
+    end
   end
 
   def convert_inline_callout node