[fix] Django 5.2: Updated CSS to fix styling of collapsable fieldset

On Django 5.2, the heading for collapsable fieldset were not
rendered in OpenWISP colors.

Author: pandafy

Diff for: openwisp_utils/admin_theme/static/admin/css/openwisp.css

@@ -158,12 +158,16 @@ a.section:visited:focus,
 .module caption,
 .inline-group h2,
 fieldset.module h2,
+#content-main fieldset.module summary,
 .selector .selector-available-title,
 .selector .selector-chosen-title {
   background: #f9f9f9;
   color: #333;
   padding: 15px;
 }
+#content-main fieldset.module summary {
+  border-color: var(--hairline-color);
+}
 table thead th.sorted .sortoptions a.sortremove:focus:after,
 table thead th.sorted .sortoptions a.sortremove:hover:after,
 a:link,
@@ -877,7 +881,7 @@ input[type="button"]:hover,
 .title-wrapper h2::after {
   content: ")";
 }
-#content.title-wrapper .object-tools {
+#content .title-wrapper .object-tools {
   margin-top: -4px;
   margin-bottom: 20px;
 }