Disable background page scrolling when modals are open.

props celloexpressions.
fixes #29074.

git-svn-id: https://develop.svn.wordpress.org/trunk@29346 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/css/common.css

@@ -218,6 +218,10 @@ body.iframe {
 	padding-top: 1px;
 }
 
+body.modal-open {
+	overflow: hidden;
+}
+
 iframe,
 img {
 	border: 0;

src/wp-admin/css/themes.css

@@ -409,10 +409,6 @@
 	z-index: 10;
 }
 
-body.theme-overlay-open {
-	overflow: hidden;
-}
-
 .theme-overlay .theme-header {
 	position: absolute;
 	top: 0;