Fix dropdown menu header and mobile view (#33108)

![image](https://github.com/user-attachments/assets/3f831c8c-ef87-4282-880a-c2738f3e1d17)

----

![image](https://github.com/user-attachments/assets/c4c0519b-cfa6-42b4-bd28-205ee514eb34)

----

![image](https://github.com/user-attachments/assets/8624a605-9f2b-4905-9cbc-0af073972874)

templates/user/dashboard/navbar.tmpl

@@ -12,7 +12,7 @@
 					{{svg "octicon-triangle-down" 14 "dropdown icon tw-ml-1"}}
 				</span>
 				<div class="context user overflow menu">
-					<div class="ui header">
+					<div class="header">
 						{{ctx.Locale.Tr "home.switch_dashboard_context"}}
 					</div>
 					<div class="scrolling menu items">
@@ -56,7 +56,7 @@
 					</span>
 					{{svg "octicon-triangle-down" 14 "dropdown icon"}}
 					<div class="context user overflow menu">
-						<div class="ui header">
+						<div class="header">
 							{{ctx.Locale.Tr "home.filter_by_team_repositories"}}
 						</div>
 						<div class="scrolling menu items">