Set new block button bg-secondary class

Author: rsmithlal

app/views/better_together/pages/_form.html.erb

@@ -139,7 +139,7 @@
           <div class="accordion accordion-flush my-3" id="new-page-block-choices">
             <div class="accordion-item">
               <h2 class="accordion-header" id="add-block-heading">
-                <button class="accordion-button collapsed btn btn-success" type="button" data-bs-toggle="collapse" data-bs-target="#available-block-types" aria-expanded="false" aria-controls="available-block-types">
+                <button class="accordion-button collapsed bg-secondary btn btn-success" type="button" data-bs-toggle="collapse" data-bs-target="#available-block-types" aria-expanded="false" aria-controls="available-block-types">
                   Add Block
                 </button>
               </h2>