Draw message list separate with CSS

Instead of a thick bar drawn in Cairo (I think?), the separator should just be drawn with CSS. The following is what I use in elementary theme:

ConversationListView {
    -GtkWidget-focus-line-width: 1px;
    -GtkTreeView-grid-line-width: 0;
}

ConversationListView.view.cell {
    border-style: solid;
    border-width: 0 0 1px 0;
    border-color: alpha (#000, 0.2);
}

ConversationListView.view.cell:selected {
    border-style: solid;
    border-width: 0 0 1px 0;
    border-color: shade (@selected_bg_color, 0.8);
}