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/**
 * Implements hook_form_system_theme_settings_alter() for views templates.
*/
function lng_tracker_form_system_theme_settings_alter(array &$form, FormStateInterface $form_state) {
  $form['options_settings'] = [
    '#type' => 'fieldset',
    '#title' => t('Theme Specific Settings'),
  ];

  $form['options_settings']['add_logo'] = [
    '#type' => 'managed_file',
    '#title' => t('Additional logo (Large)'),
    '#upload_location' => 'public://logo/',
    '#default_value' => theme_get_setting('add_logo'),
    '#states' => [
      'visible' => [
        ':input[name="File_type"]' => ['value' => t('Upload Your File')],
      ],
    ],
  ];
  $form['#submit'][] = '_lng_tracker_form_system_theme_settings_submit';
}

function _lng_tracker_form_system_theme_settings_submit(&$form, FormStateInterface &$form_state, $form_id = NULL) {
    if ($file_id = $form_state->getValue(['add_logo', '0'])) {
        $file = \Drupal::entityTypeManager()->getStorage('file')->load($file_id);
        $file->setPermanent();
        $file->save();
    }
}