From b05529d52dd4d5bf4245af5be08800f80376bcfd Mon Sep 17 00:00:00 2001
From: Kristiyan Kostadinov <crisbeto@abv.bg>
Date: Tue, 5 Aug 2025 11:43:53 +0200
Subject: [PATCH] fix(material/autocomplete): default to transparent backdrop

The autocomplete was leaving the `backdropClass` as undefined which meant that it would default to a dark one, if the user opted into it having a backdrop.

Fixes #31614.
---
 src/material/autocomplete/autocomplete-trigger.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/material/autocomplete/autocomplete-trigger.ts b/src/material/autocomplete/autocomplete-trigger.ts
index 7ddf9fc79ef4..942637ca6c4e 100644
--- a/src/material/autocomplete/autocomplete-trigger.ts
+++ b/src/material/autocomplete/autocomplete-trigger.ts
@@ -912,7 +912,7 @@ export class MatAutocompleteTrigger
       width: this._getPanelWidth(),
       direction: this._dir ?? undefined,
       hasBackdrop: this._defaults?.hasBackdrop,
-      backdropClass: this._defaults?.backdropClass,
+      backdropClass: this._defaults?.backdropClass || 'cdk-overlay-transparent-backdrop',
       panelClass: this._overlayPanelClass,
       disableAnimations: this._animationsDisabled,
     });