problem with center content

Hi
Can you please be more specific? Don’t exactly understand what you mean (your link is broken so not helpful). If you need center align content on your page – you have button Align Center in your Text Editor

@andy sorry but the website is hosted in my personal pc..
look at this screenshoot

View post on imgur.com

For static pages you have simple way to do this – just select Fullwidth Page template in Page Attributes meta box on Edit Page Screen.

For single post, blog pages and blog archives this process will be more difficult. 1st question in that case – what you planning do with sidebar? Move its below other content on page?

@ andy i delete the sidebar ..
just post box centered no sidebar..
thanks for replay

First off all I recommend you to create your own child theme for Duena (for safety editing template files, you can find tutorial here – https://codex.www.ads-software.com/Child_Themes).

Then, if you need centered content only on single post page – copy into your child theme file single.php, open it in editor and find string <div id="primary" class="span8 <?php echo esc_attr( of_get_option('blog_sidebar_pos') ) ?>">. Then change it to
<div id="primary" class="span12 <?php echo esc_attr( of_get_option('blog_sidebar_pos') ) ?>">
If you need all pages with center content – find all files wich contains this string and replace it with <div id="primary" class="span12 <?php echo esc_attr( of_get_option('blog_sidebar_pos') ) ?>">

But it’s not good idea, because a lot of styles in theme adapted to two columns structure and some elements after that manipulations can look not good