Got it:

script: /* Open Add new style dialog */ var gd = moi.geometryDatabase; gd.styleEditorOpened(); var dialog = moi.ui.createDialog( 'EditStyleDialog.htm?titleid=Add style dialog title&index=-1', '', moi.ui.mainWindow ); if ( dialog.window.doModal() != -1 ) { var styles = gd.getObjectStyles(); if ( styles.length > 0 ) moi.ui.propertiesPanel.editStyleIndex( styles.length - 1 ); } gd.styleEditorClosed();