diff --git a/public/index.html b/public/index.html
index 7c2a1cc9..7898f1d2 100644
--- a/public/index.html
+++ b/public/index.html
@@ -1,4 +1,4 @@
-<!DOCTYPE html>
+<!doctype html>
 <html>
   <head>
     <% if (VUE_APP_HTTPS) { %><script>if(location.protocol==='http:')location.protocol='https:';</script><% } %>
@@ -17,7 +17,7 @@
       <div id="container">
         <noscript><strong>Please enable javascript.</strong></noscript>
         <div id="app"></div>
-        <footer id="footer" class="mdui-text-center mdui-hidden">
+        <footer id="footer" class="mdui-text-center" hidden>
           <div class="mdui-typo no-sl">Made with ❤️ by <a href="https://github.com/Tsuk1ko" target="_blank">神代綺凛</a></div>
           <div class="mdui-text-color-theme-divider" style="font-size: 12px; margin: -2px 0 6px 0"><%= VUE_APP_DIST_VERSION %></div>
         </footer>
diff --git a/src/main.js b/src/main.js
index 262edb1c..24f58ac0 100644
--- a/src/main.js
+++ b/src/main.js
@@ -352,7 +352,7 @@ new Vue({
     this.updateScreenWidth();
     window.addEventListener('resize', _.throttle(this.updateScreenWidth, 500, { leading: false }));
     window.addEventListener('orientationchange', this.updateScreenWidth);
-    $('#footer').removeClass('mdui-hidden');
+    $('#footer').removeAttr('hidden');
   },
   i18n,
 }).$mount('#app');
