Can not sanitize select control in customize api

The add_setting logic cant find the my_theme_sanitize_select function, you need to tell it where it is:

'sanitize_callback'    => array( $this, 'my_theme_sanitize_select' ),

remember that your function is inside a class so it cant just be accessed, add this to your class:

public function my_theme_sanitize_select( $input, $setting ) {
    $from_parent = my_theme_sanitize_select( $input, $setting );
    return $from_parent;
}