I have the same problem as described in Palette does not render arrows since Wicket 7.x.x
The example includes a link with the href palette-ver-48087C00867DD23918CC93E129A02A8D.css.
How can I include the css file from 1) an imported jar file, or 2) from the web?
In the demo page for the Wicket Examples the Palette component uses DefaultTheme behavior to contribute palette.css. You could use your own Behavior to contribute custom theme.