diff --git a/manage/import-export.js b/manage/import-export.js
index a3db48b9..4f742f77 100644
--- a/manage/import-export.js
+++ b/manage/import-export.js
@@ -209,6 +209,7 @@ async function importFromString(jsonString) {
       contents: $create('#import', report.length ? report : t('importReportUnchanged')),
       buttons: [t('confirmClose'), numChanged && t('undo')],
       onshow: bindClick,
+      className: 'center',
     })
       .then(({button}) => {
         if (button === 1) {
diff --git a/manage/updater-ui.js b/manage/updater-ui.js
index 1380d72d..77893cac 100644
--- a/manage/updater-ui.js
+++ b/manage/updater-ui.js
@@ -224,6 +224,7 @@ async function showUpdateHistory(event) {
   messageBoxProxy.show({
     title: t('updateCheckHistory'),
     contents: log,
+    className: 'center',
     blockScroll: true,
     buttons: [
       t('confirmOK'),