diff --git a/core/misc/dialog.theme.css b/core/misc/dialog.theme.css
index 2480fea0035b839d3b5fb77b68aacd181553bbc1..837e49f63d8ce692e97c8cde8bf20aa7c1d87460 100644
--- a/core/misc/dialog.theme.css
+++ b/core/misc/dialog.theme.css
@@ -11,6 +11,11 @@
   border: solid 1px #ccc;
   padding: 0;
 }
+@media all and (max-width: 48em) { /* 768px */
+  .ui-dialog {
+    width: 92% !important;
+  }
+}
 .ui-dialog .ui-dialog-titlebar {
   font-weight: bold;
   background: #f3f4ee;
diff --git a/core/themes/seven/css/components/dialog.theme.css b/core/themes/seven/css/components/dialog.theme.css
index 0c99474e4293c53999c66a09fe827c7be46ef8ba..4fbe56b15da0e59baa57c0acc245c45b61ebaca6 100644
--- a/core/themes/seven/css/components/dialog.theme.css
+++ b/core/themes/seven/css/components/dialog.theme.css
@@ -10,6 +10,11 @@
   overflow: visible;
   padding: 0;
 }
+@media all and (max-width: 48em) { /* 768px */
+  .ui-dialog {
+    width: 92% !important;
+  }
+}
 .ui-dialog .ui-dialog-titlebar {
   background: #6b6b6b;
   border-top-left-radius: 5px;