CSS

Download and install a Bootstrap theme. Modify the following at
vi bootstrap/templates/menu/system/form-element.func.php

　
/**
* Overrides theme_form_element().
*/
function bootstrap_form_element(&$variables) {
$element = &$variables['element'];
$name = !empty($element['#name']) ? $element['#name'] : FALSE;
$type = !empty($element['#type']) ? $element['#type'] : FALSE;
$checkbox = $type && $type === 'checkbox';
$radio = $type && $type === 'radio';

li:before {
position: absolute;
top: 0;
left: 0;
font-family: 'FontAwesome'; /* Specify FontAwesome */
content: '\f07b'; /* This is a folder icon */
color: #fab100; /* Yellow */
}