diff --git a/src/General/Main.coffee b/src/General/Main.coffee
index 66052a1f2..25ac4d6aa 100644
--- a/src/General/Main.coffee
+++ b/src/General/Main.coffee
@@ -185,11 +185,13 @@ Main =
     styleSheets    = $$ 'link[rel="alternate stylesheet"]', d.head
     setStyle = ->
       $.rmClass doc, style
+      style = null
       for styleSheet in styleSheets
         if styleSheet.href is mainStyleSheet?.href
           style = styleSheet.title.toLowerCase().replace('new', '').trim().replace /\s+/g, '-'
           break
-      $.addClass doc, style
+      if style
+        $.addClass doc, style
     setStyle()
     return unless mainStyleSheet
     new MutationObserver(setStyle).observe mainStyleSheet,
diff --git a/src/css/style.css b/src/css/style.css
index 8b3b17569..96ba04a98 100644
--- a/src/css/style.css
+++ b/src/css/style.css
@@ -2,6 +2,7 @@
 .dialog {
   border: 1px solid;
   display: block;
+  background-color: inherit;
 }
 .dialog:not(#qr):not(#thread-watcher):not(#header-bar) {
   box-shadow: 0 1px 2px rgba(0, 0, 0, .15);