nodered_cfg/node_modules/node-red-dashboard/nodes/locales/en-US/ui_spacer.html

<script type="text/html" data-help-name="ui_spacer">
    <p>If a <b>Class</b> is specified, it will be added to the parent card. This way you can style the card and the elements inside it with custom CSS. The Class can be set at runtime by setting a <code>msg.className</code> string property.</p>
</script>