Fix flash message for flex-container (go-gitea#30657)

Author: wxiaoguang

templates/admin/layout_head.tmpl

@@ -1,11 +1,9 @@
 {{template "base/head" .ctxData}}
 <div role="main" aria-label="{{.ctxData.Title}}" class="page-content {{.pageClass}}">
-	<div class="ui container">
-		{{template "base/alert" .ctxData}}
-	</div>
 	<div class="ui container fluid padded flex-container">
 		{{template "admin/navbar" .ctxData}}
 		<div class="flex-container-main">
+			{{template "base/alert" .ctxData}}
 			{{/* block: admin-setting-content */}}
 
 {{if false}}{{/* to make html structure "likely" complete to prevent IDE warnings */}}

templates/user/dashboard/dashboard.tmpl

@@ -1,9 +1,9 @@
 {{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">
 		<div class="flex-container-main">
+			{{template "base/alert" .}}
 			{{template "user/heatmap" .}}
 			{{template "user/dashboard/feeds" .}}
 		</div>

web_src/css/base.css

@@ -495,12 +495,6 @@ 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]),