Where do the section input fields values are stored in database

Question

 register_setting('Y-sidebar-options','picture');

where do the option group name stored in database .

Answer 1

The option group (1st param to register_setting()) is not stored anywhere. The only use for option groups is to output a couple of hidden fields and a nonce, via a call to settings_fields().

Answer 2

The options which you store by using the function register_setting is saved in table wp_options.

Answer 3

Look for the add_setting('Y-sidebar-options'…); call. Settings go into the wp_options table and can be either under a field by it's own name or else a theme_mod (default).

Pls also see: https://codex.wordpress.org/Class_Reference/WP_Customize_Manager/add_setting