style(dark): Adjust chat bubble background color(langgenius#20990)

- Changed the chat bubble background color from #a5bddb to #27314d
- This modification provides better visual appearance and readability for the chat bubble in dark theme

web/themes/dark.css

@@ -386,7 +386,7 @@ html[data-theme="dark"] {
   --color-background-gradient-bg-fill-chat-bg-2: #1d1d20;
   --color-background-gradient-bg-fill-chat-bubble-bg-1: #c8ceda14;
   --color-background-gradient-bg-fill-chat-bubble-bg-2: #c8ceda05;
-  --color-background-gradient-bg-fill-chat-bubble-bg-3: #a5bddb;
+  --color-background-gradient-bg-fill-chat-bubble-bg-3: #27314d;
   --color-background-gradient-bg-fill-debug-bg-1: #c8ceda14;
   --color-background-gradient-bg-fill-debug-bg-2: #18181b0a;