Background in content and centering

I’m remaking this site: Old Site . I’m having two problems. I’m trying to put a background image that is the full width ONLY in the content area. Here is my site: My SITE. I didn’t save the changes but I figured out how to make the page full width even though my website doesn’t show that. I found a way to add a background image however the image covers the whole wordpress page not just the content area. I couldn’t find anything to show me how to do that.

I tried doing something like this in the page.php file that didn’t work

<img src="url" class="logo">
<?php get_template_part('templates/page', 'header'); ?>
<?php get_template_part('templates/content', 'page'); ?>

also tried doing something like this in the css:
#content { background }

My second question is how do I center my info. As you can see from the old site and then mine. I created a div class around my content like this

<div class="the_content">
<?php get_template_part('templates/content', 'page'); ?>
</div>

I was able to put a red background color around my content but, I needed help on centering it. I played with the width looking at tutorials but couldn’t figure it out. Thanks