Using a `GtkListBox` allows us to make more complex widgets when trying
to showcase an icon theme. For example, we can make the example icon a
bit bigger so you don't have to squeeze your eyes to distinsguish them
one from another.
Other possibilities we can do with this widget, is for example making
the folder label clickable to open the file explorer, or add a flat
button at the end with the same purpose. Since it's now just a
`GtkLabel`, we can also make the path selectable (for copy-pasting).
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