Use the same background color as the editor for SharedScreen

styles/src/styleTree/sharedScreen.ts

@@ -0,0 +1,9 @@
+import { ColorScheme } from "../themes/common/colorScheme";
+import { background } from "./components";
+
+export default function sharedScreen(colorScheme: ColorScheme) {
+  let layer = colorScheme.highest;
+  return {
+    background: background(layer)
+  }
+}