diff --git a/js/dom.js b/js/dom.js
index a308498c..86ebf7c6 100644
--- a/js/dom.js
+++ b/js/dom.js
@@ -555,7 +555,7 @@ async function waitForSheet({
     if (el) {
       event.preventDefault();
       window.messageBoxProxy.show({
-        className: 'note',
+        className: 'note center-dialog',
         contents: el.dataset.title || el.title,
         buttons: [t('confirmClose')],
       });
diff --git a/manage/filters.js b/manage/filters.js
index ad53d320..f5fe5f77 100644
--- a/manage/filters.js
+++ b/manage/filters.js
@@ -36,7 +36,7 @@ function initFilters() {
   $('#search-help').onclick = event => {
     event.preventDefault();
     messageBoxProxy.show({
-      className: 'help-text',
+      className: 'help-text center-dialog',
       title: t('search'),
       contents:
         $create('ul',
diff --git a/manage/sorter.js b/manage/sorter.js
index 9a181e47..97963e54 100644
--- a/manage/sorter.js
+++ b/manage/sorter.js
@@ -189,7 +189,7 @@ const sorter = (() => {
   async function showHelp(event) {
     event.preventDefault();
     messageBoxProxy.show({
-      className: 'help-text',
+      className: 'help-text center-dialog',
       title: t('sortStylesHelpTitle'),
       contents:
         $create('div',