diff --git a/static/app.css b/static/app.css
index e723ab3..f9924e9 100644
--- a/static/app.css
+++ b/static/app.css
@@ -20,6 +20,11 @@
 
 * { box-sizing: border-box; }
 
+/* The UA's [hidden] { display: none } loses to any class that sets display
+   (e.g. .drop-overlay's flex), which left the overlay permanently covering the
+   page. Make the attribute win everywhere. */
+[hidden] { display: none !important; }
+
 html, body {
   margin: 0;
   height: 100%;