Background image not appearing

custom background can be used in below way:

  $defaults = array(
  'default-color'          => '',
  'default-image'          => '',
  'default-repeat'         => '',
  'default-position-x'     => '',
  'default-attachment'     => '',
  'wp-head-callback'       => '_custom_background_cb',
  'admin-head-callback'    => '',
  'admin-preview-callback' => ''
  );
 add_theme_support( 'custom-background', $defaults );

Example usage:

 $args = array(
  'default-color' => '000000',
  'default-image' => '%1$s/images/testback.jpg',
 );

add_theme_support( 'custom-background', $args );

Example output when you will view source:

 <style type="text/css" id="custom-background-css"> body.custom-background { background-color: #bdd96e; }

For details follow link:

Output:

Thanks!