target maintenance content independently of decorative icons

app/layouts/default.vue

@@ -430,7 +430,7 @@ useHead(() => ({
       class="maintenance-banner"
     >
       <Icon name="lucide:triangle-alert" aria-hidden="true" />
-      <span>{{
+      <span class="maintenance-message">{{
         site.config.value?.maintenance_mode_message ||
         "站点维护中，部分功能可能不可用。"
       }}</span>