title: GTK TreeView styling
body: <p>Short version:  What CSS selector can be used to style the background of a GTK TreeView header?</p>
  
  <p>Long version:  I've tried <code>treeview header</code>, <code>treeview header .button</code>, <code>.button</code>, <code>button</code>, <code>label</code>, <code>GtkTreeView header</code>, <code>header</code> and <code>*</code> as selectors for the header of a Gtk.TreeView.  Of these, <code>button</code> works to change the colour of the text in the header (the <code>color</code> attribute) but not the background (<code>background-color</code>).  <code>label</code> changes the colour of the background behind the header text, but leaves a big area around the text at the default.  <code>*</code> works, but of course changes everything else, too.  </p>