Dropdown categories stay on selected option

I have a custom drop down that displays custom taxonomy in a hierarchical format. One drop down has all of the top level items and then that triggers a second drop down to appear. How can I have the drop downs stay on the selected option once it is selected? Here is my code.

<?php $args = array(
    'show_option_all'    => '',
    'show_option_none'   => '',
    'orderby'            => 'name',
    'order'              => 'ASC',
    'show_count'         => 1,
    'hide_empty'         => 1,
    'child_of'           => 0,
    'parent'             => 0,
    'exclude'            => '',
    'echo'               => 1,
    'selected'           => 0,
    'hierarchical'       => 0,
    'name'               => 'cat',
    'id'                 => '',
    'class'              => 'postform',
    'depth'              => 1,
    'tab_index'          => 0,
    'taxonomy'           => 'classification',
    'hide_if_empty'      => false,
    'walker'             => ''
); 

$tax_menu_items = get_categories( $args ); ?>