WIP: adapt reference-version to dark mode

This is not quite the best way to do it; Rather, the offending CSS in
`man-pages.scss` should be modified to use a centrally-defined CSS
custom property instead of a hard-coded color.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

assets/sass/dark-mode.css

@@ -68,6 +68,10 @@
                 text-decoration: dashed 1px underline;
             }
 
+            #reference-version {
+                background-color: rgba(111, 110, 105, 0.33);
+            }
+
             #documentation #main div.verseblock pre.content {
                 color: var(--light-font-color);
                 background-color: #5e5951;