n_oct/plugins/rainlab/builder/controllers/index/_plugin-selector.php

<div class="layout control-scrollpanel">
    <div class="layout-cell">
        <div class="layout-relative" id="builder-plugin-selector-panel">
            <form class="layout" onsubmit="return false">
                <?= $this->widget->pluginList->render() ?>
            </form>
        </div>
    </div>
</div>