Source

File: wp-includes/class-wp-customize-nav-menus.php

protected function print_custom_links_available_menu_item() {
		?>
		<div id="new-custom-menu-item" class="accordion-section">
			<h4 class="accordion-section-title" role="presentation">
				<?php _e( 'Custom Links' ); ?>
				<button type="button" class="button-link" aria-expanded="false">
					<span class="screen-reader-text"><?php _e( 'Toggle section: Custom Links' ); ?></span>
					<span class="toggle-indicator" aria-hidden="true"></span>
				</button>
			</h4>
			<div class="accordion-section-content customlinkdiv">
				<input type="hidden" value="custom" id="custom-menu-item-type" name="menu-item[-1][menu-item-type]" />
				<p id="menu-item-url-wrap" class="wp-clearfix">
					<label class="howto" for="custom-menu-item-url"><?php _e( 'URL' ); ?></label>
					<input id="custom-menu-item-url" name="menu-item[-1][menu-item-url]" type="text" class="code menu-item-textbox" placeholder="https://">
				</p>
				<p id="menu-item-name-wrap" class="wp-clearfix">
					<label class="howto" for="custom-menu-item-name"><?php _e( 'Link Text' ); ?></label>
					<input id="custom-menu-item-name" name="menu-item[-1][menu-item-title]" type="text" class="regular-text menu-item-textbox">
				</p>
				<p class="button-controls">
					<span class="add-to-menu">
						<input type="submit" class="button submit-add-to-menu right" value="<?php esc_attr_e( 'Add to Menu' ); ?>" name="add-custom-menu-item" id="custom-menu-item-submit">
						<span class="spinner"></span>
					</span>
				</p>
			</div>
		</div>
		<?php
	}