ot_typo3/ot_templating/Resources/Private/Layouts/Backend/Default.html

{namespace v=FluidTYPO3\Vhs\ViewHelpers}

<f:be.container includeCssFiles="{ot_customizer: '{f:uri.resource(path:\'assets/Backend/style/ot_customizer.css\')}'}">
    <div class="ot-templating">
        <f:render section="content" />
    </div>
</f:be.container>