Source

File: wp-includes/theme.php

function remove_theme_mods() {
	delete_option( 'theme_mods_' . get_option( 'stylesheet' ) );

	// Old style.
	$theme_name = get_option( 'current_theme' );
	if ( false === $theme_name ) {
		$theme_name = wp_get_theme()->get( 'Name' );
	}
	delete_option( 'mods_' . $theme_name );
}