MainWindow.glade (Código)

<?xml version="1.0" encoding="UTF-8"?>
<!-- Generated with glade 3.38.2 -->
<interface>
    <requires lib="gtk+" version="3.24"/>
    <object class="GtkApplicationWindow" id="MainWindow">
        <property name="can_focus">False</property>
        <property name="default_width">683</property>
        <property name="default_height">384</property>
        <property name="title" translatable="yes">Gtk.CssProvider</property>
        <property name="icon">../../../assets/icons/icon.png</property>
        <child>
            <placeholder/>
        </child>
        <child>
            <object class="GtkBox" id="vbox">
                <property name="visible">True</property>
                <property name="can_focus">False</property>
                <property name="orientation">vertical</property>
                <property name="border_width">12</property>
                <child>
                    <object class="GtkEntry" id="entry">
                        <property name="visible">True</property>
                        <property name="can_focus">True</property>
                        <property name="placeholder_text" translatable="yes">Digite algo</property>
                    </object>
                    <packing>
                        <property name="expand">False</property>
                        <property name="fill">True</property>
                        <property name="position">0</property>
                    </packing>
                </child>
                <child>
                    <object class="GtkLabel" id="label">
                        <property name="visible">True</property>
                        <property name="can_focus">False</property>
                        <property name="label" translatable="yes">Este texto será alterado!</property>
                    </object>
                    <packing>
                        <property name="expand">True</property>
                        <property name="fill">True</property>
                        <property name="position">1</property>
                    </packing>
                </child>
                <child>
                    <object class="GtkButton" id="button">
                        <property name="label" translatable="yes">Clique Aqui</property>
                        <property name="visible">True</property>
                        <property name="can_focus">True</property>
                        <property name="receives_default">True</property>
                        <signal name="clicked" handler="_on_button_clicked" swapped="no"/>
                    </object>
                    <packing>
                        <property name="expand">False</property>
                        <property name="fill">True</property>
                        <property name="position">2</property>
                    </packing>
                </child>
            </object>
        </child>
    </object>
</interface>