How do I make preview button open local dev server?

I’m testing out theiaide/theia-docker. If I have something like express or nginx running, how can I point the preview pane to the local server? Right now it just opens, and doesn’t allow me to change the URL. Is there a way to configure this button to open a specific URL by default?

There should be Open URL... command.

@akosyakov is there a way to configure what happens the preview button on the right is pressed? Or would that have to be done with an extension?

You will need to write Theia extension and call