If you want to change the icon of a marker and the icon window is hidden behind the map when clicking the “Change” button for icons, this is usually caused by a plugin conflict (some plugins do not follow best practices and embedd their javascripts and CSS files on every admin page and not just where needed).
You can either find and disable the plugin causing this or add the following code at the end your
theme´s functions.php to fix this:
/* Maps Marker Pro - fix for icon modal being hidden by other plugins or themes using jquery ui */
function mmp_icon_modal_visibility_workaround() {
$current_screen = get_current_screen();
if ( ($current_screen->base == 'maps-marker-pro_page_mapsmarkerpro_marker') || ($current_screen->base == 'maps-marker-pro_page_mapsmarkerpro_map') ) {
echo '<style>.ui-dialog { z-index: 99999 !important; }</style>';
}
}
add_action('admin_head', 'mmp_icon_modal_visibility_workaround');