theme: darken vignette

- instead of locally boxing in search results, darken the whole overview

Addresses https://gitlab.gnome.org/GNOME/gnome-shell/issues/288

data/theme/gnome-shell-sass/_common.scss

@@ -1349,9 +1349,6 @@ StScrollBar {
 
   #searchResultsBin {
     max-width: 1000px;
-    background-color: $osd_bg_color;
-    padding: 2em;
-    border-radius: 16px;
   }
 
   #searchResultsContent {

js/ui/lightbox.js

@@ -7,7 +7,7 @@ const Params = imports.misc.params;
 const Tweener = imports.ui.tweener;
 
 var DEFAULT_FADE_FACTOR = 0.4;
-var VIGNETTE_BRIGHTNESS = 0.8;
+var VIGNETTE_BRIGHTNESS = 0.2;
 var VIGNETTE_SHARPNESS = 0.7;
 
 const VIGNETTE_DECLARATIONS = '\