Remove the grey background behind streamfields

wagtail/admin/static_src/wagtailadmin/scss/layouts/page-editor.scss

@@ -270,7 +270,6 @@
 
     // cursory styling for streamfield. Main styling in client/src/components/StreamField/StreamField.scss
     &.stream-field {
-        background-color: #f6f6f6;
         padding-left: 20px;
         padding-right: 20px;