Set background color to transparent in module and page file cmp

lib/js/src/compose/types/module-field/file.ts

@@ -45,7 +45,7 @@ const defaults = (): Readonly<FileOptions> => Object.freeze({
   maxWidth: '',
   borderRadius: '',
   margin: 'auto',
-  backgroundColor: '',
+  backgroundColor: '#FFFFFF00',
 })
 
 export class ModuleFieldFile extends ModuleField {

lib/js/src/compose/types/page-block/file.ts

@@ -37,7 +37,7 @@ const defaults: Readonly<Options> = Object.freeze({
   maxWidth: '',
   borderRadius: '',
   margin: 'auto',
-  backgroundColor: '',
+  backgroundColor: '#FFFFFF00',
   magnifyOption: '',
   clickToView: true,
   enableDownload: true