testsuite/css/change/test3.ui

<?xml version="1.0" encoding="UTF-8"?>
<interface>
  <object class="GtkWindow" id="window1">
    <property name="can_focus">False</property>
    <property name="decorated">0</property>
    <child>
      <object class="GtkBox">
        <property name="visible">True</property>
        <child>
          <object class="GtkLabel">
            <property name="visible">True</property>
            <property name="label" translatable="yes">Hello World!</property>
          </object>
        </child>
        <child>
          <object class="GtkLabel">
            <property name="visible">True</property>
            <property name="label" translatable="yes">Hello World!</property>
            <style><class name="test"/></style>
          </object>
        </child>
      </object>
    </child>
  </object>
</interface>