diff --git a/themes/tiddlywiki/vanilla/base.tid b/themes/tiddlywiki/vanilla/base.tid
index 5ad721f0a..07d930e9d 100644
--- a/themes/tiddlywiki/vanilla/base.tid
+++ b/themes/tiddlywiki/vanilla/base.tid
@@ -878,6 +878,16 @@ canvas.tw-edit-bitmapeditor  {
 ** Modals
 */
 
+.modal-wrapper {
+	position: fixed;
+	overflow: auto;
+	overflow-y: scroll;
+	top: 0;
+	right: 0;
+	bottom: 0;
+	left: 0;
+}
+
 .modal-backdrop {
 	position: fixed;
 	top: 0;
@@ -910,11 +920,9 @@ canvas.tw-edit-bitmapeditor  {
 
 @media (min-width: 55em) {
 	.modal {
-		position: fixed;
-		top: 50%;
-		left: 50%;
-		width: 560px;
-		margin: -180px 0 0 -280px;
+		position: relative;
+		width: 50%;
+		margin: 30px auto;
 	}
 }