Update app.py

app.py

@@ -17,12 +17,14 @@ css = """
 }
 .message-bubble-border {
     border-radius: 6px !important;
+}
+.dark.message-bubble-border {
     border-color: #21293b !important;
 }
-.user.dark {
+.dark.user {
     background: #1e293b !important;
 }
-.assistant.dark, .pending.dark {
+.dark.assistant, .dark.pending {
     background: #0f172a !important;
 }
 """