diff --git a/.changeset/fix-dialog-dark-theme-selector.md b/.changeset/fix-dialog-dark-theme-selector.md
new file mode 100644
index 0000000000..287278d3a5
--- /dev/null
+++ b/.changeset/fix-dialog-dark-theme-selector.md
@@ -0,0 +1,7 @@
+---
+'@backstage/ui': patch
+---
+
+Fixed dark mode background for Dialog component by correcting the theme attribute selector from `data-theme` to `data-theme-mode`.
+
+**Affected components:** Dialog
diff --git a/packages/ui/src/components/Dialog/Dialog.module.css b/packages/ui/src/components/Dialog/Dialog.module.css
index b6d26b3f3d..b6d98446e5 100644
--- a/packages/ui/src/components/Dialog/Dialog.module.css
+++ b/packages/ui/src/components/Dialog/Dialog.module.css
@@ -30,7 +30,7 @@
     z-index: 1000;
   }
 
-  [data-theme='dark'] .bui-Dialog {
+  [data-theme-mode='dark'] .bui-Dialog {
     background: rgba(0, 0, 0, 0.5);
   }