Codeigniter Slug

Try this:
// The order is important

$routes->get('/(:any)/(:any)/(:any)', 'FrontPanel::details/$1/$2/$3', ['namespace' => 'BasicApp\FrontPanel\Controllers']);

$routes->get('/(:any)/(:any)', 'FrontPanel::details/$1/$2', ['namespace' => 'BasicApp\FrontPanel\Controllers']);

$routes->get('/(:any)/(:any)/(:any)', 'FrontPanel::details/$1/$2/$3', ['namespace' => 'BasicApp\FrontPanel\Controllers']);

$routes->get('/(:any)', 'FrontPanel::details/$1', ['namespace' => 'BasicApp\FrontPanel\Controllers']);