Ticket #41155: 41155.6.diff

src/wp-admin/css/themes.css

@@ -11 +11 @@
         overflow-y: scroll;
 }
 
+.themes-php #adminmenuwrap {
+        z-index: 10001; /* above Theme Overlay */
+}
+
 body.js .theme-browser.search-loading {
         display: none;
 }
@@ -372 +376 @@
         background: #f0f0f1;
         background: rgba(240, 240, 241, 0.9);
         z-index: 10000; /* Over WP Pointers. */
+        min-height: calc(100vh - var(--wp-admin--admin-bar--height, 32px));
 }
 
 .theme-overlay .theme-header {