fix styles for React

Author: GoodDayForSurf

packages/devextreme-cli/src/templates/react/application/src/dx-styles.scss

@@ -38,10 +38,10 @@ body {
       margin: 0;
       line-height: 40px;
     }
+  }
 
-    .screen-x-small & {
-      padding: 20px;
-    }
+  .screen-x-small .content {
+    padding: 20px;
   }
 
   .container {