Adjust background color of user message buttons and timestamp

wwwroot/css/chat.css

@@ -482,6 +482,11 @@
   white-space: nowrap;
 }
 
+.msg.user button,
+.msg.user .msg-timestamp {
+  background: var(--f2-bg);
+}
+
 .msg-timestamp {
   padding: .25em .6em;
   border-radius: var(--border-radius);