The use-symbolic property of type :boolean (Read / Write)
Whether to use symbolic icons as the icons. Note that if the symbolic icons
are not available in your installed theme, then the normal, potentially colorful icons will be used. Default value: false
Details
The gtk-volume-button class is a subclass of the gtk-scale-button class that has been tailored for use as a volume
control widget with suitable icons, tooltips and accessible labels.