DOC: Reduce horizontal padding on small screens (#12465)

Maximize used horizontal space when the screen is small.

Author: timhoffm

doc/_themes/sphinx13/static/sphinx13.css

@@ -442,6 +442,8 @@ div.viewcode-block:target {
     }
     div.body {
         border-left: none;
+        padding-left: 0.5em;
+        padding-right: 0.5em;
     }
 }