add announcement bar to docs and minor styling update

packages/mermaid/src/docs/.vitepress/components/TopBar.vue

@@ -1,6 +1,6 @@
 <template>
   <div
-    class="w-full top-bar bg-gradient-to-r from-[#bd34fe] to-[#ff3670] flex items-center text-center justify-center p-1 text-white"
+    class="mb-4 w-full top-bar bg-gradient-to-r from-[#bd34fe] to-[#ff3670] flex items-center text-center justify-center p-1 text-white"
   >
     <p class="flex-grow text-center tracking-wide text-text">
       <a

packages/mermaid/src/docs/.vitepress/theme/index.ts

@@ -25,6 +25,7 @@ export default {
       'home-hero-before': () => h(TopBar),
       'home-hero-info-before': () => h(ProductHuntBadge),
       'home-features-after': () => h(HomePage),
+      'doc-before': () => h(TopBar),
     });
   },
   enhanceApp({ app, router }: EnhanceAppContext) {