fix(ast): the background image cannot be displayed when viewing the program

src/views/bigscreen/ast/Viewer.vue

@@ -60,7 +60,7 @@
     >
       <div
         class="c-viewer__background has-bg"
-        :style="backgroundStyle"
+        :style="backgroundStyles"
       />
       <widget
         v-for="(item, index) in widgets"