i want change h2 tag of dynamic sidebar.but before_title not work.

i want change h2 element of dynamic sidebar.
i think it not good for search engine.

before_widget and after_widget key work well with the code written below.
but before_title and after_title key not work.
please tell me the some advice.

# sidebar.php
<?php dynamic_sidebar( 'sidebar1' ); ?>

# function.php

if (function_exists('register_sidebar')) {
		register_sidebar(array(
	   'name' => 'sidebar_one',
	   'id' => 'sidebar1',
	   'description' => 'this is sidebar1',
	   'before_widget'=>'<nav class="sidebar__wrapper">',
	   'after_widget'=>'</nav>',
	   'before_title'=>'<h2 class="sidebar__title">',
	   'after_title'=>'</h2>',));
	   }

# image of result

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