Exactly the same as Select control.
The only difference is that the field will show a list of your pages. As a result, you don’t have to manually define the choices argument.
The default value for dropdown-pages controls can be a page ID (int).
Example: 'default' => 42, The returned value is the ID of the selected page.
Example
new \Kirki\Field\Dropdown_Pages(
[
'settings' => 'dropdown_pages_setting',
'label' => esc_html__( 'Dropdown Pages', 'kirki' ),
'section' => 'section_id',
'default' => 42,
'priority' => 10,
]
);