3x4 grid on drupal

grid.css

.grid-wrapper ul li {
    list-style: none;
    float: left;
    display: block;
    width: 32%;
    margin-right: 1%;
}

.grid-wrapper ul li img {
    max-width: 100%;

}

.row-of-three {
    width: 100%;
    display: block;
    float: left;
}

.row-of-three li {
    list-style: none;
}

grid.php

<?php
/**
 * Implements hook_menu().
 */
function grid_menu() {
    $items['testme'] = array(
        'page callback' => 'grid_print_items',
        'access arguments' => array('access content'),
        'type' => MENU_CALLBACK,
    );
    return $items;
}

/**
 * Implements menu callback.
 */
function grid_get_items() {
    drupal_add_css(drupal_get_path('module', 'grid') . '/css/grid.css', array('weight' => 10, 'group' => CSS_THEME,));
    $query = new EntityFieldQuery();
    $query->entityCondition('entity_type', 'node')
        ->entityCondition('bundle', 'article')
        ->propertyCondition('status', 1)
        ->fieldCondition('field_number', 'value', 0, '>')
        ->fieldCondition('field_number', 'value', 13, '<')
        ->fieldOrderBy('field_number', 'value', 'ASC');
    $result = $query->execute();
    $grid_items = array();
    if (isset($result['node'])) {
        $grid_items_nids = array_keys($result['node']);
        $grid_items = entity_load('node', $grid_items_nids);
    }
    return $grid_items;
}

function grid_print_items() {
    $grid_items = grid_get_items();
    return theme('grid_items', array("grid_items" => $grid_items));
}

/**
 * Implements hook_node_presave().
 */
function grid_node_presave($node) {
    $grid_items = grid_get_items();
    $current_number = $node->field_number['und'][0]['value'];
    if (is_numeric($current_number) && $current_number > 0 && $current_number < 13) {
        foreach ($grid_items as $grid_item) {
            $grid_item_number = $grid_item->field_number['und'][0]['value'];
            if ($node->nid != $grid_item->nid && $grid_item_number == $current_number) {
                $grid_item->field_number['und'][0]['value']++;
                node_save($grid_item);
            }
        }
    }
}

/**
 * Implements hook_theme().
 */
function grid_theme($existing, $type, $theme, $path) {
    return array(
        'grid_items' => array(
            'template' => 'tpl/grid_items', 
            'arguments' => array('grid_items' => null), 
        ),
    );
}

grid_items.tpl.php

<div class="grid-wrapper">
    <ul>
        <?php $i = 0; ?>
        <?php foreach ($grid_items as $grid_item): ?>
            <?php $i++; ?>
            <?php ($i % 3 == 1) ? print '<div class="row-of-three">' : ''; ?>
            <li class="grid-item">
                <h1> <?php print $grid_item->title; ?> </h1>
                <a href="<?php print drupal_get_path_alias("node/" . $grid_item->nid); ?>">
                    <img src="<?php print file_create_url($grid_item->field_image['und'][0]['uri']); ?>">
                </a>
            </li>
            <?php ($i % 3 == 0) ? print '</div>' : ''; ?>
        <?php endforeach; ?>
    </ul>
</div>