Improve warnings style in mkdocs

Author: ewels

README.md

@@ -2,6 +2,10 @@
 
 ## 📚 Docs 👉🏻 <https://nextflow-io.github.io/nf-validation>
 
+!!! warning
+
+<div class="admonition warning" markdown>
+
 <!-- prettier-ignore -->
 > [!IMPORTANT]
 > **`nf-validation` has now been renamed to `nf-schema`. The `nf-validation` plugin will not receive any future updates.**
@@ -13,6 +17,8 @@
 > plugins { id 'nf-schema@2.0.0' }
 > ```
 
+</div>
+
 **A Nextflow plugin to work with validation of pipeline parameters and sample sheets.**
 
 ## Introduction

overrides/main.html

@@ -1,5 +1,8 @@
 {% extends "base.html" %}
 
 {% block announce %}
-  <div>nf-validation has been deprecated. Please use <a href="https://nextflow-io.github.io/nf-schema/latest/">nf-schema</a> instead.</div>
-{% endblock %}
+  <div style="text-align: center;">
+    <strong>nf-validation has been deprecated.</strong>
+    Please use <a href="https://nextflow-io.github.io/nf-schema/latest/">nf-schema</a> instead.
+  </div>
+{% endblock %}