Add getThemeCSS to file sink and file source

packages/file-handling/src/file-sink.js

@@ -154,6 +154,7 @@ export class FileSink extends ScopedElementsMixin(DBPLitElement) {
     static get styles() {
         // language=css
         return css`
+            ${commonStyles.getThemeCSS()}
             ${commonStyles.getGeneralCSS()}
             ${commonStyles.getButtonCSS()}
             ${commonStyles.getModalDialogCSS()}

packages/file-handling/src/file-source.js

@@ -325,6 +325,7 @@ export class FileSource extends ScopedElementsMixin(DBPLitElement) {
     static get styles() {
         // language=css
         return css`
+            ${commonStyles.getThemeCSS()}
             ${commonStyles.getGeneralCSS()}
             ${commonStyles.getButtonCSS()}
             ${commonStyles.getModalDialogCSS()}