Issue #3521647: Fix 'Open Category' button visibility in Categories Listing paragraph

The "Open Category" button in the Categories Listing paragraph has the same color for both background and text, making the label unreadable.

Steps to Reproduce

• Create a Program node.
• Add a Categories Listing paragraph.
• Save and view the node.
• The nodes (type Program Subcategory) are rendered through a View, each with an "Open Category" button.

Expected Result

The button should have proper contrast:

• White background
• Blue text

Before: After:

templates/node--view--categories-listing.html.twig

@@ -85,6 +85,6 @@ set classes = [
   <div class="col-md-7 content">
     <h2>{{ label }}</h2>
     {{ content.field_category_description }}
-    <a href="{{ url }}" class="btn btn-primary outline d-block d-lg-inline-block" aria-label="{{ node.label }} {{ 'read more'|t }}">{{ 'Open category'|t }}</a>
+    <a href="{{ url }}" class="btn btn-outline-primary d-block d-lg-inline-block" aria-label="{{ node.label }} {{ 'read more'|t }}">{{ 'Open category'|t }}</a>
   </div>
 </article>