--- /dev/null
+/**
+ * Implements hook_system_themes_page_alter().
+ */
+function {{ machine_name }}_system_themes_page_alter(&$theme_groups) {
+ foreach ($theme_groups as $state => &$group) {
+ foreach ($theme_groups[$state] as &$theme) {
+ // Add a foo link to each list of theme operations.
+ $theme->operations[] = [
+ 'title' => t('Foo'),
+ 'url' => Url::fromRoute('system.themes_page'),
+ 'query' => ['theme' => $theme->getName()]
+ ];
+ }
+ }
+}