A style stored GDK resources to be used when drawing widgets, and, thus, can be used to customize the appearance of the application. Although it is possible to change the style of the widget programmatically, it is advisable instead to rely on the .rc (resource) files so that the customization is left up to the user.

Structure of GtkStyle
<?php
  class GtkStyle {
      GdkColor  $black;
      GdkColor  $white;

      GdkGC     $black_gc;
      GdkGC     $white_gc;
      
      GdkFont   $font;

      GdkColor  $fg[5];
      GdkColor  $bg[5];
      GdkColor  $light[5];
      GdkColor  $dark[5];
      GdkColor  $mid[5];
      GdkColor  $text[5];
      GdkColor  $base[5];

      GdkGC     $fg_gc[5];
      GdkGC     $bg_gc[5];
      GdkGC     $light_gc[5];
      GdkGC     $dark_gc[5];
      GdkGC     $mid_gc[5];
      GdkGC     $text_gc[5];
      GdkGC     $base_gc[5];

      GdkPixmap $bg_pixmap[5];
  }

?>
'black' and 'white' colors simply stored the corresponding colors for easy access. Same goes for 'black_gc' and 'white_gc'.

The rest of the arrays all have 5 elements each, corresponding to 5 possible widget states: normal, active, prelight, selected, and insensitive. So, if the widget is prelighted (cursor over it), its foreground color may be different than normal and can be accessed as $style->fg[GTK_STATE_PRELIGHT].

Foreground and background are self-explanatory. Light/mid/dark normally contain values that are automatically computed from fg/bg ones. Text is drawn using 'text' and 'base' colors.