CSS tweaks to warning/error segments and misc fixes (#13024)

* CSS tweaks to warning/error segments and misc fixes

- Adjust styling for warning/error in arc-green
- Change danger boxes from orange to red
- Fix code highlight text color in arc-green
- Fix warning message in arc-green
- Fix border in org member list in arc-green
- Fix disabled checkbox text in arc-green

* use same selector in gitea theme

* fix blame highlight

Co-authored-by: zeripath <art27@cantab.net>

templates/user/settings/account.tmpl

@@ -167,10 +167,10 @@
 			</form>
 			</div>
 		</div>
-		<h4 class="ui top attached warning header">
+		<h4 class="ui top attached error header">
 			{{.i18n.Tr "settings.delete_account"}}
 		</h4>
-		<div class="ui attached warning segment">
+		<div class="ui attached error segment">
 			<div class="ui red message">
 				<p class="text left">{{svg "octicon-alert"}} {{.i18n.Tr "settings.delete_prompt" | Str2html}}</p>
 			</div>