In GTK+ 3.0, GTK+ was added GtkStyleContext to replace GtkStyle and the theming infrastructure available in 2.x. GtkStyleContext is an object similar in spirit to GtkStyle, as it contains theming information, although in a more complete and tokenized fashion. Moving to #GtkStyleContext is twofold, there is themes and theming engines on one side, and applications, widgets and libraries on the other. From GTK+ 3.0 on, theme engines must implement #GtkThemingEngine and be installed in $(libdir)/gtk+-3.0/$(GTK_VERSION)/theming-engines, and the files containing style information must be written in the CSS format as parsed by #GtkCssProvider. For a theme named "Clearlooks", the CSS file parsed by default would be $(sharedir)/themes/Clearlooks/gtk-3.0/gtk.css, with possible variants such as the dark theme being named as "gtk-dark.css" in the same directory. Migrating a #GtkStyle based engine to a #GtkThemingEngine based one should be straightforward for most of the vmethods. Besides a cleanup in the available paint methods and a cleanup in the parameters passed (in favor of #GtkStyleContext containing all the information), the available render methods should resemble those of #GtkStyle quite evidently, with some differences worth to point out: All variations of draw_box(), draw_flat_box(), draw_shadow(), draw_box_gap() and draw_shadow_gap() become replaced by render_background(), render_frame() and render_frame_gap(), where the first would render frameless backgrounds and the last two would render all frame variants. draw_resize_grip() disappears in favor of render_handle() with a #GTK_STYLE_CLASS_GRIP class set in the style context. draw_spinner() disappears in favor of render_activity() with a #GTK_STYLE_CLASS_SPINNER class set in the style context. The available list of render methods is: gtk_render_background(): Renders a widget/area background. gtk_render_frame(): Renders a frame border around the given rectangle. Usually the detail of the border depends on the theme information, plus the current widget state. gtk_render_layout(): Renders a #PangoLayout gtk_render_frame_gap(): Renders a frame border with a gap on one side. gtk_render_handle(): Renders all kind of handles and resize grips, usually depending the rendering on the CSS class. gtk_render_check() and gtk_render_option(): Respectively render checkboxes and radiobuttons. gtk_render_arrow(): Renders an arrow pointing to a direction gtk_render_expander(): Renders an expander indicator, such as in #GtkExpander gtk_render_focus(): Renders the indication that a widget has the keyboard focus gtk_render_line(): Renders a line from one coordinate to another. gtk_render_slider(): Renders a slider indicator, such as in #GtkScale gtk_render_extension(): Renders and extension to an UI element, such as a notebook tab. gtk_render_activity(): Renders an area displaying activity, be it a progressbar or a spinner. gtk_render_icon_pixbuf(): Renders an icon into a #GdkPixbuf. One of the main differences to #GtkStyle engines is that the rendered widget is totally isolated from the theme engine, all style information is meant to be retrieved from the #GtkThemingEngine API, or from the #GtkWidgetPath obtained from gtk_theming_engine_get_path(), which fully represents the rendered widget's hierarchy from a styling point of view. The detail string available in the old engines is now essentially replaced by widget regions and CSS classes and widget regions. Regions are a way for container/complex widgets to classify and add ordering hints to its children. CSS classes identify are a way to label some content being rendered, both regions and classes can be identified both in CSS files and theming engines. There are several predefined classes and regions such as %GTK_STYLE_CLASS_BUTTON or %GTK_STYLE_REGION_TAB in gtkstylecontext.h, although custom widgets may define their own, which themes may attempt at handling. If there is a need for extending the default CSS parser, #GtkRCStyle has been replaced by gtk_theming_engine_register_property(), where the theming engine may register new properties that map to a #GType, even if there is builtin support for most basic types, it is possible to hook a custom parser for the property. The installed properties depend on the #GtkThemeEngine::name property, so they should be added in the constructed() handler. For example, if an engine with the name "Clearlooks" installs a "focus-color" property, the property -Clearlooks-focus-color will be registered and accepted in CSS. Widget style properties also follow a similar syntax, with the widget type name used as a prefix, so for example the #GtkWidget:focus-line-width style property could be modified in CSS as -GtkWidget-focus-line-width. The difference in syntax between the RC and CSS file formats is evident, it actually seems shorter to highlight the similarities, although anyone familiar with CSS3 should get an idea soon of the new format, to make a more or less comprehensive example, the following RC data: style "default" { xthickness = 1 ythickness = 1 GtkButton::child-displacement-x = 1 GtkButton::child-displacement-y = 1 GtkCheckButton::indicator-size = 14 bg[NORMAL] = @bg_color bg[PRELIGHT] = shade (1.02, @bg_color) bg[SELECTED] = @selected_bg_color bg[INSENSITIVE] = @bg_color bg[ACTIVE] = shade (0.9, @bg_color) fg[NORMAL] = @fg_color fg[PRELIGHT] = @fg_color fg[SELECTED] = @selected_fg_color fg[INSENSITIVE] = darker (@bg_color) fg[ACTIVE] = @fg_color text[NORMAL] = @text_color text[PRELIGHT] = @text_color text[SELECTED] = @selected_fg_color text[INSENSITIVE] = darker (@bg_color) text[ACTIVE] = @selected_fg_color base[NORMAL] = @base_color base[PRELIGHT] = shade (0.95, @bg_color) base[SELECTED] = @selected_bg_color base[INSENSITIVE] = @bg_color base[ACTIVE] = shade (0.9, @selected_bg_color) engine "clearlooks" { colorize_scrollbar = TRUE style = CLASSIC } } style "tooltips" { xthickness = 4 ythickness = 4 bg[NORMAL] = @tooltip_bg_color fg[NORMAL] = @tooltip_fg_color } style "button" { xthickness = 3 ythickness = 3 bg[NORMAL] = shade (1.04, @bg_color) bg[PRELIGHT] = shade (1.06, @bg_color) bg[ACTIVE] = shade (0.85, @bg_color) } style "entry" { xthickness = 3 ythickness = 3 bg[SELECTED] = mix (0.4, @selected_bg_color, @base_color) fg[SELECTED] = @text_color engine "clearlooks" { focus_color = shade (0.65, @selected_bg_color) } } style "other" { bg[NORMAL] = #fff; } class "GtkWidget" style "default" class "GtkEntry" style "entry" widget_class "*<GtkButton>" style "button" widget "gtk-tooltip*" style "tooltips" widget_class "window-name.*.GtkButton" style "other" would roughly translate to this CSS: * { padding: 1; -GtkButton-child-displacement-x: 1; -GtkButton-child-displacement-y: 1; -GtkCheckButton-indicator-size: 14; background-color: @bg_color; color: @fg_color; -Clearlooks-colorize-scrollbar: true; -Clearlooks-style: classic; } *:hover { background-color: shade (@bg_color, 1.02); } *:selected { background-color: @selected_bg_color; color: @selected_fg_color; } *:insensitive { color: shade (@bg_color, 0.7); } *:active { background-color: shade (@bg_color, 0.9); } .tooltip { padding: 4; background-color: @tooltip_bg_color; color: @tooltip_fg_color; } .button { padding: 3; background-color: shade (@bg_color, 1.04); } .button:hover { background-color: shade (@bg_color, 1.06); } .button:active { background-color: shade (@bg_color, 0.85); } .entry { padding: 3; background-color: @base_color; color: @text_color; } .entry:selected { background-color: mix (@selected_bg_color, @base_color, 0.4); -Clearlooks-focus-color: shade (0.65, @selected_bg_color) } /* The latter selector is an specification of the first, since any widget may use the same classes or names */ #window-name .button, GtkWindow#window-name GtkButton.button { background-color: #fff; } One notable difference is the reduction from fg/bg/text/base colors to only foreground/background, in exchange the widget is able to render its various elements with different CSS classes, so they would be themed independently. It is worth mentioning that the new file format doesn't support custom keybindings nor stock icon mappings as the RC format did. When porting your widgets to use #GtkStyleContext, this is usually the checklist to follow: Replace style_set() calls with style_updated(). Try to identify the role of what you're rendering with any number of classes, this will replace the detail string, there is a predefined set of CSS classes. Note that complex widgets will probably need rendering different elements with different applying CSS classes in order to have them styled separatedly. This could result in code like (simplified examples): static void gtk_button_init (GtkButton *button) { GtkStyleContext *context; ... context = gtk_widget_get_style_context (GTK_WIDGET (button)); /* Set the "button" class */ gtk_style_context_add_class (context, GTK_STYLE_CLASS_BUTTON); } Or static gboolean gtk_spin_button_draw (GtkSpinButton *spin, cairo_t *cr) { GtkStyleContext *context; ... context = gtk_widget_get_style_context (GTK_WIDGET (spin)); gtk_style_context_save (context); gtk_style_context_add_class (context, GTK_STYLE_CLASS_ENTRY); /* Call to entry draw impl with "entry" class */ parent_class->draw (spin, cr); gtk_style_context_restore (context); gtk_style_context_save (context); /* Render up/down buttons with the "button" class */ gtk_style_context_add_class (context, GTK_STYLE_CLASS_BUTTON); draw_up_button (spin, cr); draw_down_button (spin, cr); gtk_style_context_restore (context); ... } Note that #GtkStyleContext only provides fg/bg colors, so text/base is done through distinctive theming of the different classes. For example, An entry would usually be black on white while a button would usually be black on light grey. Replace all gtk_paint_*() calls to use gtk_render_*(), the most distinctive changes are the use of #GtkStateFlags to represent the widget state and the lack of #GtkShadowType. For gtk_render_check() and gtk_render_option(), the shadow_type parameter is replaced by the #GTK_STATE_FLAG_ACTIVE and #GTK_STATE_FLAG_INCONSISTENT state flags. For things such as pressed/unpressed button states, #GTK_STATE_FLAG_ACTIVE is used, so the CSS may style normal/active states differently to render outset/inset borders respectively. Replace all uses of xthickness/ythickness, #GtkStyleContext uses the CSS box model, so there is the border-width/padding/margin properties to replace the different applications of X and Y thickness. Note that all of this is merely a guideline to use, which widgets may choose to obey or not. As a consequence of the RC format going away, calling gtk_rc_parse() or gtk_rc_parse_string() won't be doing anything to the widget styling, the way to replace these calls is using the CSS format, which is loaded through a #GtkCssProvider, and inserted as a style resource to an individual widget through gtk_style_context_add_provider() or to all widgets in a screen through gtk_style_context_add_provider_for_screen(). Notice that you can also get style information from custom resources by implementing a #GtkStyleProvider, where it would be translated to something the widget understands. Although this is an advanced feature that should be rarely used. There are some features in #GtkStyleContext that weren't available in #GtkStyle, or were made available over time for certain widgets through extending the detail string in obscure ways. UI elements being rendered may be provided now a lot more information, so going through this list you'll ensure your widget is the perfect citizen in a fully themable UI If your widget renders a series of similar elements, such as tabs in a #GtkNotebook or rows/column in a #GtkTreeView, consider adding regions through gtk_style_context_add_region(), these regions can be referenced in CSS and the :nth-child pseudoclass may be used to match the elements depending on the flags passed. GtkNotebook tab { background-color: #f3329d; } GtkTreeView row::nth-child (even) { background-color: #dddddd; } If your container renders child widgets within different regions, make it implement GtkContainer::get_path_for_child(), This function lets containers assign special #GtkWidgetPaths to child widgets depending on its role/region, this is necessary to extend the concept above throughout the widget hierarchy. For example, a #GtkNotebook would modify the tab labels' #GtkWidgetPath so the "tab" region is added, doing this so would allow the tab label to be themed through: GtkNotebook tab GtkLabel { font: Sans 8; } If you intend several visual elements to look interconnected, make sure you specify rendered elements' connection areas through gtk_style_context_set_junction_sides() #GtkStyleContext supports implicit animations on state changes for the most simple cases, widgets with one single animatable area, which are changed state through gtk_widget_set_state_flags() or gtk_widget_unset_state_flags(). These functions trigger the animations for the affected state flags. If your widget consists of more than a simple area (such as buttons or entries), and these different areas may be rendered with different states, make sure to mark the rendered areas through gtk_style_context_push_animatable_region() and gtk_style_context_pop_animatable_region(). gtk_style_context_notify_state_change() may be used to trigger a transition for a given state, the region ID will determine the animatable region that becomes affected by this transition.