Issue #3354755: Use CSS only accordion and support nested

Closes #3354755

src/Plugin/Shortcode/AccordionShortcode.php

@@ -25,6 +25,8 @@ class AccordionShortcode extends ShortcodeBase {
     $icon = isset($attributes['icon']) && $attributes['icon'] ? '<i class="' . $attributes['icon'] . '"></i> ' : '';
     $attributes['class'] = $attributes['class'] ?? '';
     $attributes['class'] .= " accordion-item";
+    $title = $attributes['title'] ?? '';
+    $attributes['title'] = strip_tags($title);
     $id = uniqid();
     $output = [
       '#theme' => 'shortcode_accordion',
@@ -32,7 +34,7 @@ class AccordionShortcode extends ShortcodeBase {
       '#text' => $text ,
       '#id' => $id ,
       '#icon' => $icon ,
-      '#title' => $attributes['title'],
+      '#title' => $title,
     ];
     return $this->render($output);