Hi Daniel, you could add it under Additional HTML here :
https://<yoursite>/admin/settings.php?section=additionalhtml
<style type="text/css">
#page-navbar > nav.breadcrumb-button > a{
background-color: green; // for example
}
</style>
This should change the turn editing on button background color to green . Beware - if it does work this WILL change the background color of that button on your site live !
Hittesh