How to add a class around.

add_class_example.php

function hook_preprocess_entity(&$variables) {
  if ($variables['content_element']->type == 'tour_item') {
    $content_element_wrapper = entity_metadata_wrapper('content_element', $variables['content_element']);
    $value = $content_element_wrapper->field_text_position->value();
    
    // Add some class to the tour item wrapper. Decide dependent on the value above.
    $variables['classes_array'][] = 'text-left';
  }
}