Custom CSS Styling

Thanks @tverbeke, @fmichielssen. This is yet another useful feature.

I would like to remove the black navbar once signed in, to give my Shiny app a simpler (cleaner) look. I think this can be achieved by commenting out:
<div th:replace="../fragments/navbar :: navbar"></div>
in app.html.

This would require moving the log-out button into the Shiny app, which I think can be done as follows:
includeHTML("logoutbutton.html")
where logoutbutton.html contains:
<a class='btn btn-default action-button' th:href="@{/logout}">Log out</a>

The button appears fine, but it appears the Thymeleaf link doesn’t work. Is this because the Shiny app is in an iframe that can’t “see” its parent framework? Is there a way around this?