Thank you for your reply.
I have set the theme of the page template to "-- no theme --", but the LayoutsBasics.css is still being loaded.
If that was not the case, I could add the bundles style to your Master page as you described by using a placeholder, but now it won't render correctly.
I have followed the steps described here: http://www.sitefinity.com/developer-network/knowledge-base/details/how-to-disable-the-built-in-css-styles-loaded-by-the-default-basic-theme
However, this page also indicates that it will still inject CSS: "however there will still be a little amount that we keep injecting in order to keep page content rendering properly"
When I open the site with the developer tools, and comment the LayoutBasics CSS, the site displays correctly.
Do you know if it's possible to update the settings so no standard-CSS will be loaded?
I have no experience with Feather yet, so I will look into it.