flash (macromedia): I'm trying to customize a listbox and a scroll pane.

In MX you could click though the compnent's nested parts (through the
Library). Then when you got to the white square set its alpha to zero. But I
think MX2004 "simplified" all this by making customization sort of css-like,
and transparent might not be an option.

Does anyone know about this?

For the curious, I found out about Themes:

Flash MX 2004 ships with two themes: "haloTheme.fla" and "sampleTheme.fla"
(you can find those in the First Run > ComponentFLA folder of your installation
directory).

In the Library panel there's a whole bunch of folders and if you browse down
through Flash UI Components 2 >Themes > MMDefault you'll find the folders that
contain the assets for each of the UI components (Accordion Assets, Alert
Assets, etc.).

You can now simply edit those movieclips and make all the changes you want.
When you're done with modifying the component assets, simply drag that folder
from the Themes FLA to the stage of the FLA you want to apply the skins to. You
can then safely delete those assets from the stage of your FLA.