FIX Switch Add Existing from jQuery UI to use Bootstrap styles

src/GridFieldAddExistingSearchButton.php

@@ -91,14 +91,15 @@ class GridFieldAddExistingSearchButton implements GridField_HTMLProvider, GridFi
     {
         GridFieldExtensions::include_requirements();
 
-        $data = new ArrayData(array(
+        $data = ArrayData::create([
             'Title' => $this->getTitle(),
-            'Link'  => $grid->Link('add-existing-search')
-        ));
+            'Classes' => 'action btn btn-primary font-icon-search add-existing-search',
+            'Link' => $grid->Link('add-existing-search'),
+        ]);
 
-        return array(
-            $this->fragment => $data->renderWith('Symbiote\\GridFieldExtensions\\GridFieldAddExistingSearchButton'),
-        );
+        return [
+            $this->fragment => $data->renderWith(__CLASS__),
+        ];
     }
 
     public function getURLHandlers($grid)

templates/Symbiote/GridFieldExtensions/GridFieldAddExistingSearchButton.ss

@@ -1,3 +1,3 @@
-<a href="$Link" class="action ss-ui-button ui-button add-existing-search" data-icon="magnifier">
-	$Title
-</a>
+<a href="$Link" class="$Classes">
+    <span class="btn__title">$Title</span>
+</a>