Small & colorful indicator label for Gtk

app.css

/* Support for colored labels.
 * These are sometimes handy in order to highlight errors
 * or mark some entries with "xx new items".
 */ 

#AppIndicatorLabelError,
#AppIndicatorLabelSuccess,
#AppIndicatorLabelWarning,
#AppIndicatorLabelTheme {
    /* Animate changes so the label color gets faded in */
    transition-property: color, border-color, background-color;
    transition: 250ms ease-in-out;

    /* More readable on colored background */
    text-shadow: None;
    color: @theme_selected_fg_color;

    /* Make the shape round and give it enough space */
    border-radius: 4px;
    padding: 1px 6px;

    /* Add a small border around the label */
    border-style: outset;
    border-width: 2px;
}

/* This will look pretty much like a normal label.
 * Just include a fix for doing the blending right.
 */
#AppIndicatiorLabelEmpty {
    border-color: alpha(white, 0);
}

/* That's probably a dumb way to find the colors.
 * We inherit the theme colors and try to modify them
 * so they fit our needs. A hue-changing functions would be nice.
 *
 * See here for reference on the used theme colors:
 * https://gitorious.org/gtk-theme/adwaita-clean-dark/source/master:gtk-3.0/gtk.css
 */

@define-color indicator_label_error   
    alpha(mix(@error_color, @theme_selected_fg_color, 0.3), 0.9);
@define-color indicator_label_success 
    alpha(mix(shade(@success_color, 0.85), @theme_selected_fg_color, 0.3), 0.9);
@define-color indicator_label_warning  
    alpha(mix(@warning_color, @theme_selected_fg_color, 0.3), 0.9);
@define-color indicator_label_theme 
    mix(@theme_selected_bg_color, @theme_selected_fg_color, 0.3);

#AppIndicatorLabelError {
    background-color: @indicator_label_error;
    border-color: alpha(mix(@indicator_label_error, @theme_selected_fg_color, 0.66), 0.5);
}

#AppIndicatorLabelSuccess {
    background-color: @indicator_label_success;
    border-color: alpha(mix(@indicator_label_success, @theme_selected_fg_color, 0.66), 0.5);
}

#AppIndicatorLabelWarning {
    background-color: @indicator_label_warning;
    border-color: alpha(mix(@indicator_label_warning, @theme_selected_fg_color, 0.66), 0.5);
}

#AppIndicatorLabelTheme {
    background-color: @indicator_label_theme;
    border-color: alpha(mix(@indicator_label_theme, @theme_selected_fg_color, 0.66), 0.5);
}

indicator.py

class IndicatorLabel(Gtk.Label):
    """A label that has a rounded, colored background.

    It is mainly useful for showing new entries or indicate errors.
    There are 3 colors available, plus a color derived from the
    theme's main color. In case of Adwaita blue.
    """
    SUCCESS, WARNING, ERROR, THEME = range(1, 5)

    def __init__(self, *args):
        Gtk.Label.__init__(self, *args)
        self.set_use_markup(True)

        # Do not expand space.
        self.set_valign(Gtk.Align.CENTER)
        self.set_halign(Gtk.Align.CENTER)
        self.set_vexpand(False)
        self.set_hexpand(False)

        # Use the theme's color by default.
        self.set_color(IndicatorLabel.THEME)

    def set_color(self, state):
        classes = {
            IndicatorLabel.ERROR: 'AppIndicatorLabelError',
            IndicatorLabel.SUCCESS: 'AppIndicatorLabelSuccess',
            IndicatorLabel.WARNING: 'AppIndicatorLabelWarning',
            IndicatorLabel.THEME: 'AppIndicatorLabelTheme'
        }

        # Will act as normal label for invalid states.
        # Useful for highlighting problematic input.
        self.set_name(classes.get(state, 'AppIndicatorLabelEmpty'))