Default files

An application can cause GTK+ to parse a specific CSS style sheet by calling gtk_css_provider_load_from_file() and adding the provider with gtk_style_context_add_provider() or gtk_style_context_add_provider_for_screen(). In addition, certain files will be read when GTK+ is initialized. First, the file $XDG_CONFIG_HOME/gtk-3.0/gtk.css is loaded if it exists. Then, GTK+ tries to load $HOME/.themes/theme-name/gtk-3.0/gtk.css, falling back to datadir/share/themes/theme-name/gtk-3.0/gtk.css, where theme-name is the name of the current theme (see the "gtk-theme-name" setting) and datadir is the prefix configured when GTK+ was compiled, unless overridden by the GTK_DATA_PREFIX environment variable.

Style sheets

The basic structure of the style sheets understood by this provider is a series of statements, which are either rule sets or '@-rules', separated by whitespace.

A rule set consists of a selector and a declaration block, which is a series of declarations enclosed in curly braces ({ and }). The declarations are separated by semicolons (;). Multiple selectors can share the same declaration block, by putting all the separators in front of the block, separated by commas.

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GtkButton, GtkEntry {
    color: #ff00ea;
    font: Comic Sans 12
}

Selectors

Selectors work very similar to the way they do in CSS, with widget class names taking the role of element names, and widget names taking the role of IDs. When used in a selector, widget names must be prefixed with a '#' character. The '*' character represents the so-called universal selector, which matches any widget.

To express more complicated situations, selectors can be combined in various ways:

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/* Theme labels that are descendants of a window */
GtkWindow GtkLabel {
    background-color: #898989
}

/* Theme notebooks, and anything that's within these */
GtkNotebook {
    background-color: #a939f0
}

/* Theme combo boxes, and entries that
 are direct children of a notebook */
GtkComboBox,
GtkNotebook > GtkEntry {
    color: @fg_color;
    background-color: #1209a2
}

/* Theme any widget within a GtkBin */
GtkBin * {
    font-name: Sans 20
}

/* Theme a label named title-label */
GtkLabel#title-label {
    font-name: Sans 15
}

/* Theme any widget named main-entry */
#main-entry {
    background-color: #f0a810
}

Widgets may also define style classes, which can be used for matching. When used in a selector, style classes must be prefixed with a '.' character.

Refer to the documentation of individual widgets to learn which style classes they define and see the section called “Style classes and regions” for a list of all style classes used by GTK+ widgets.

Note that there is some ambiguity in the selector syntax when it comes to differentiation widget class names from regions. GTK+ currently treats a string as a widget class name if it contains any uppercase characters (which should work for more widgets with names like GtkLabel).

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/* Theme all widgets defining the class entry */
.entry {
    color: #39f1f9;
}

/* Theme spinbuttons' entry */
GtkSpinButton.entry {
    color: #900185
}

In complicated widgets like e.g. a GtkNotebook, it may be desirable to style different parts of the widget differently. To make this possible, container widgets may define regions, whose names may be used for matching in selectors.

Some containers allow to further differentiate between regions by applying so-called pseudo-classes to the region. For example, the tab region in GtkNotebook allows to single out the first or last tab by using the :first-child or :last-child pseudo-class. When used in selectors, pseudo-classes must be prefixed with a ':' character.

Refer to the documentation of individual widgets to learn which regions and pseudo-classes they define and see the section called “Style classes and regions” for a list of all regions used by GTK+ widgets.

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/* Theme any label within a notebook */
GtkNotebook GtkLabel {
    color: #f90192;
}

/* Theme labels within notebook tabs */
GtkNotebook tab GtkLabel {
    color: #703910;
}

/* Theme labels in the any first notebook
 tab, both selectors are equivalent */
GtkNotebook tab:nth-child(first) GtkLabel,
GtkNotebook tab:first-child GtkLabel {
    color: #89d012;
}

Another use of pseudo-classes is to match widgets depending on their state. This is conceptually similar to the :hover, :active or :focus pseudo-classes in CSS. The available pseudo-classes for widget states are :active, :prelight (or :hover), :insensitive, :selected, :focused and :inconsistent.

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/* Theme active (pressed) buttons */
GtkButton:active {
    background-color: #0274d9;
}

/* Theme buttons with the mouse pointer on it,
   both are equivalent */
GtkButton:hover,
GtkButton:prelight {
    background-color: #3085a9;
}

/* Theme insensitive widgets, both are equivalent */
:insensitive,
*:insensitive {
    background-color: #320a91;
}

/* Theme selection colors in entries */
GtkEntry:selected {
    background-color: #56f9a0;
}

/* Theme focused labels */
GtkLabel:focused {
    background-color: #b4940f;
}

/* Theme inconsistent checkbuttons */
GtkCheckButton:inconsistent {
    background-color: #20395a;
}

Widget state pseudoclasses may only apply to the last element in a selector.

To determine the effective style for a widget, all the matching rule sets are merged. As in CSS, rules apply by specificity, so the rules whose selectors more closely match a widget path will take precedence over the others.

@ Rules

GTK+'s CSS supports the @import rule, in order to load another CSS style sheet in addition to the currently parsed one.

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@import url ("path/to/common.css");

In order to extend key bindings affecting different widgets, GTK+ supports the @binding-set rule to parse a set of bind/unbind directives, see GtkBindingSet for the supported syntax. Note that the binding sets defined in this way must be associated with rule sets by setting the gtk-key-bindings style property.

Customized key bindings are typically defined in a separate gtk-keys.css CSS file and GTK+ loads this file according to the current key theme, which is defined by the "gtk-key-theme-name" setting.

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@binding-set binding-set1 {
  bind "<alt>Left" { "move-cursor" (visual-positions, -3, 0) };
  unbind "End";
};

@binding-set binding-set2 {
  bind "<alt>Right" { "move-cursor" (visual-positions, 3, 0) };
  bind "<alt>KP_space" { "delete-from-cursor" (whitespace, 1)
                         "insert-at-cursor" (" ") };
};

GtkEntry {
  gtk-key-bindings: binding-set1, binding-set2;
}

GTK+ also supports an additional @define-color rule, in order to define a color name which may be used instead of color numeric representations. Also see the "gtk-color-scheme" setting for a way to override the values of these named colors.

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@define-color bg_color #f9a039;

* {
    background-color: @bg_color;
}

Symbolic colors

Besides being able to define color names, the CSS parser is also able to read different color expressions, which can also be nested, providing a rich language to define colors which are derived from a set of base colors.

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@define-color entry-color shade (@bg_color, 0.7);

GtkEntry {
    background-color: @entry-color;
}

GtkEntry:focused {
    background-color: mix (@entry-color,
                           shade (#fff, 0.5),
                           0.8);
}

The various ways to express colors in GTK+ CSS are:

Gradients

Linear or radial Gradients can be used as background images.

A linear gradient along the line from (start_x, start_y) to (end_x, end_y) is specified using the syntax

where start_x and end_x can be either a floating point number between 0 and 1 or one of the special values 'left', 'right' or 'center', start_y and end_y can be either a floating point number between 0 and 1 or one of the special values 'top', 'bottom' or 'center', position is a floating point number between 0 and 1 and color is a color expression (see above). The color-stop can be repeated multiple times to add more than one color stop. 'from (color)' and 'to (color)' can be used as abbreviations for color stops with position 0 and 1, respectively.

Example 32. A linear gradient

This gradient was specified with

-gtk-gradient (linear,
               left top, right bottom,
               from(@yellow), to(@blue))

Example 33. Another linear gradient

This gradient was specified with

-gtk-gradient (linear,
               0 0, 0 1,
               color-stop(0, @yellow),
               color-stop(0.2, @blue),
               color-stop(1, #0f0))

A radial gradient along the two circles defined by (start_x, start_y, start_radius) and (end_x, end_y, end_radius) is specified using the syntax

where start_radius and end_radius are floating point numbers and the other parameters are as before.

Example 34. A radial gradient

This gradient was specified with

-gtk-gradient (radial,
               center center, 0,
               center center, 1,
               from(@yellow), to(@green))

Example 35. Another radial gradient

This gradient was specified with

-gtk-gradient (radial,
               0.4 0.4, 0.1,
               0.6 0.6, 0.7,
               color-stop (0, #f00),
               color-stop (0.1, #a0f),
               color-stop (0.2, @yellow),
               color-stop (1, @green))

Border images

Images can be used in 'slices' for the purpose of creating scalable borders.

The syntax for specifying border images of this kind is:

The sizes of the 'cut off' portions are specified with the top, right, bottom and left parameters. The 'middle' sections can be repeated or stretched to create the desired effect, by adding the 'repeat' or 'stretch' options after the dimensions. If two options are specified, the first one affects the horizontal behaviour and the second one the vertical behaviour. If only one option is specified, it affects both.

Example 36. A border image

This border image was specified with

url("gradient1.png") 10 10 10 10

Example 37. A repeating border image

This border image was specified with

url("gradient1.png") 10 10 10 10 repeat

Example 38. A stretched border image

This border image was specified with

url("gradient1.png") 10 10 10 10 stretch

Styles can specify transitions that will be used to create a gradual change in the appearance when a widget state changes. The following syntax is used to specify transitions:

The duration is the amount of time that the animation will take for a complete cycle from start to end. If the loop option is given, the animation will be repated until the state changes again. The option after the duration determines the transition function from a small set of predefined functions.

Figure 3. Linear transition

Figure 4. Ease transition

Figure 5. Ease-in-out transition

Figure 6. Ease-in transition

Figure 7. Ease-out transition

Supported properties

Properties are the part that differ the most to common CSS, not all properties are supported (some are planned to be supported eventually, some others are meaningless or don't map intuitively in a widget based environment).

There is also a difference in shorthand properties, for example in common CSS it is fine to define a font through the different font-family, font-style, font-size properties, meanwhile in GTK+'s CSS only the canonical font property is supported.

The currently supported properties are:

GtkThemingEngines can register their own, engine-specific style properties with the function gtk_theming_engine_register_property(). These properties can be set in CSS like other properties, using a name of the form

, where namespace is typically the name of the theming engine, and name is the name of the property. Style properties that have been registered by widgets using gtk_widget_class_install_style_property() can also be set in this way, using the widget class name for namespace.

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* {
    engine: clearlooks;
    border-radius: 4;
    -GtkPaned-handle-size: 6;
    -clearlooks-colorize-scrollbar: false;
}

struct GtkCssProvider

struct GtkCssProvider;

gtk_css_provider_get_default ()

GtkCssProvider *    gtk_css_provider_get_default        (void);

Returns the provider containing the style settings used as a fallback for all widgets.

gtk_css_provider_get_named ()

GtkCssProvider *    gtk_css_provider_get_named          (const gchar *name,
                                                         const gchar *variant);

Loads a theme from the usual theme paths

gtk_css_provider_load_from_data ()

gboolean            gtk_css_provider_load_from_data     (GtkCssProvider *css_provider,
                                                         const gchar *data,
                                                         gssize length,
                                                         GError **error);

Loads data into css_provider, making it clear any previously loaded information.

gtk_css_provider_load_from_file ()

gboolean            gtk_css_provider_load_from_file     (GtkCssProvider *css_provider,
                                                         GFile *file,
                                                         GError **error);

Loads the data contained in file into css_provider, making it clear any previously loaded information.

gtk_css_provider_load_from_path ()

gboolean            gtk_css_provider_load_from_path     (GtkCssProvider *css_provider,
                                                         const gchar *path,
                                                         GError **error);

Loads the data contained in path into css_provider, making it clear any previously loaded information.

gtk_css_provider_new ()

GtkCssProvider *    gtk_css_provider_new                (void);

Returns a newly created GtkCssProvider.

GTK_CSS_PROVIDER_ERROR

#define GTK_CSS_PROVIDER_ERROR (gtk_css_provider_error_quark ())

enum GtkCssProviderError

typedef enum
{
  GTK_CSS_PROVIDER_ERROR_FAILED
} GtkCssProviderError;