Update book.js

Author: expikr

src/theme/book.js

@@ -331,18 +331,22 @@ function playground_text(playground, hidden = true) {
             stylesheets.ayuHighlight.disabled = true;
             stylesheets.tomorrowNight.disabled = false;
             stylesheets.highlight.disabled = true;
-
             ace_theme = "ace/theme/tomorrow_night";
         } else if (theme == 'ayu') {
             stylesheets.ayuHighlight.disabled = false;
             stylesheets.tomorrowNight.disabled = true;
             stylesheets.highlight.disabled = true;
             ace_theme = "ace/theme/tomorrow_night";
-        } else {
+        } else if (theme == 'rust' || theme == 'light') {
             stylesheets.ayuHighlight.disabled = true;
             stylesheets.tomorrowNight.disabled = true;
             stylesheets.highlight.disabled = false;
             ace_theme = "ace/theme/dawn";
+        } else {
+            stylesheets.ayuHighlight.disabled = true;
+            stylesheets.tomorrowNight.disabled = true;
+            stylesheets.highlight.disabled = false;
+            ace_theme = "ace/theme/tomorrow_night";
         }
 
         setTimeout(function () {