Is possible to edit dimensions? (Main column, sidebar)

The short answer is: yes, you can do that with CSS. ??

The longer answer is this:

Learning how to target your site’s CSS will help you make certain design and layout changes. Here are some very helpful posts that will help you customize your site with CSS:

https://dailypost.wordpress.com/2013/07/25/css-selectors/

https://dailypost.wordpress.com/2013/06/21/css-intro/

https://dailypost.wordpress.com/2013/08/29/css-matched-rule-pane/

If CSS is new to you, here are some resources for learning more about it:

• CSS Basics
• Editing CSS
• How to Find Your Theme’s CSS

You can learn more about using media queries that target certain screen sizes here:

https://css-tricks.com/snippets/css/media-queries-for-standard-devices/
https://webdesignerwall.com/tutorials/responsive-design-with-css3-media-queries

Media queries are a simple concept but powerful in practice, and can take some experimentation and testing to get right.

There are several ways to make CSS changes.

Don’t edit the theme files directly, otherwise your changes will be overwritten when the theme is updated.

An easy way to add custom CSS is to install the Jetpack plugin and activate the Custom CSS module. You’ll then add your custom CSS in the new stylesheet editor that’ll appear in your dashboard, under Appearance > Edit CSS.

As alternatives, you could either install a standalone custom CSS plugin, or create a child theme.

Ok, i will try..
(i don’t know very good CSS, but i try..)
Thanks

I can’t find the name of the right sidebar..how can easily find it ?
thanks a lot

You can find it by right-clicking in the sidebar using a browser inspector tool:

#secondary

Editing widget-area i have got an issue..
i have done with:

.site-content {
	margin: 81px auto 0;
	max-width: 67em;
}

Could you explain what exactly you’re trying to accomplish at this point so I can know how to better help?