diff --git a/index.html b/index.html
index ca3339c..86c971a 100644
--- a/index.html
+++ b/index.html
@@ -154,6 +154,9 @@
             line-height: 1.35;
         }
 
+        /* hidden 属性が display:flex に上書きされるのを防ぐ */
+        [hidden] { display: none !important; }
+
         /* ── Markdown content ── */
         .md-body { max-width: 680px; }
         .md-body h1 { display: none; } /* h1 is shown in post-meta */