Fix flash on dashboard (#30572)

Fixes https://github.com/go-gitea/gitea/issues/30566, regression from
https://github.com/go-gitea/gitea/pull/30214.

templates/user/dashboard/dashboard.tmpl

@@ -1,8 +1,8 @@
 {{template "base/head" .}}
 <div role="main" aria-label="{{.Title}}" class="page-content dashboard feeds">
 	{{template "user/dashboard/navbar" .}}
+	{{template "base/alert" .}}
 	<div class="ui container flex-container">
-		{{template "base/alert" .}}
 		<div class="flex-container-main">
 			{{template "user/heatmap" .}}
 			{{template "user/dashboard/feeds" .}}

web_src/css/base.css

@@ -501,6 +501,12 @@ img.ui.avatar,
   margin-top: calc(var(--page-spacing) - 1rem);
 }
 
+/* add horizontal margin to elements that are outside top-level of .flex-container or .ui.container */
+.page-content > .flash-message {
+  margin-left: var(--page-margin-x);
+  margin-right: var(--page-margin-x);
+}
+
 .ui.form .fields.error .field textarea,
 .ui.form .fields.error .field select,
 .ui.form .fields.error .field input:not([type]),