GtkCellRendererProgress uses different/fewer CSS classes than GtkProgressBar
Submitted by mod..@..ush.ai
In gtk_cell_renderer_progress_render, the .trough style class is applied when rendering the trough, and the .progressbar style class is applied when rendering the actual progress (not the trough), but the usage of these does not match that of GtkProgressBar. GtkProgressBar applies .progressbar to all its rendering, and .trough and .progress (no "bar") to the subcomponents. In the cell renderer, the .progressbar class is only added to the actual progress portion of the bar, and .progress is never applied.
GtkProgressBar also applies one of the .left/.right/.top/.bottom classes while the cell renderer does not.
In addition, no .horizontal/.vertical style class is set for the orientation of GtkCellRendererProgress, which makes theming them properly in all cases virtually impossible.