Enhance WordPress customizer

functions.php

<?php
//* Enhance customizer
add_action( 'customize_register', 'nl_enhance_customizer' );
function nl_enhance_customizer( $wp_customize ) {
    $wp_customize->add_section(
        'footer_section',
        array(
            'title'         => __('Title of the settings box', 'theme_name'),
            'description'   => __('Description of the settings box'),
            'priority'      => 150,
        )
    );
    $wp_customize->add_setting(
    	'footer_textbox',
    	array(
    	    'default'       => __('Default value of the settings box', 'theme_name'),
    	)
    );
    $wp_customize->add_control(
    	'footer_textbox',
    	array(
    	    'label'         => __('Label of the control box', 'theme_name'),
    	    'description'   => __('Description of the control box'),
	    'section'       => 'footer_section',
	    'type'          => 'textarea',
        )
    );
}