Timezone customizer setting and control

timezone.php

<?php 
	/**
	 * Timezone
	 *         
	 */
	$wp_customize->add_setting( 'timezone_string', array(
		'type' 	                => 'option', 
		'sanitize_callback'     => 'sanitize_text_field',
	) );
	class Timezone_Control extends WP_Customize_Control {
		public $type = 'dbt_timezone';
	
		public function render_content() {
			$timezone = get_option( 'timezone_string' );
			$selected = esc_attr( $timezone ); ?>
			<label>
				<span class="customize-control-title"><?php esc_html_e( $this->label ); ?></span>
				<span class="description customize-control-description"><?php esc_html_e( $this->description ); ?></span>
				<select name="timezone_string" value <?php $this->link()?>>
					<?php echo wp_timezone_choice( $selected ); ?>
				</select>
			</label><?php
		} 
	}
	$wp_customize->add_control( new Timezone_Control( $wp_customize, 'timezone_string', array(
		'section'       => 'dbt_settings',
		'label'         => __( 'Timezone' ),
		'priority'      => 30,
	) ) );