Fix unusual U-A foreground/background color settings

Otherwise it ends up with dark-grey text on white while using WebKitGTK in dark GTK mode (yes, they screwed up too).

Still ending up with instance list in Statuses tab being fully white for some reason…

src/styles/index.scss

@@ -11,6 +11,8 @@ body {
   -webkit-font-smoothing: antialiased;
   text-rendering: optimizeLegibility;
   font-family: Helvetica Neue, Helvetica, PingFang SC, Hiragino Sans GB, Microsoft YaHei, Arial, sans-serif;
+  background: #FFF;
+  color: #000;
 }
 
 label {