whmcsProxmoxCloud/app/UI/Home/Templates/pages/vmBuild.tpl

<div class="alert alert-warning" role="alert">
    <button type="button" class="close" data-dismiss="alert"></button>
    <p>{$customTplVars.warning}</p>
    {if $customTplVars.warningMessage}<p>{$customTplVars.warningMessage}</p>{/if}
</div>