align header with content

I built a website with subdomains and subdirectories using a thematic child theme. (1.0.2.1). I added a widget to the header. The header looked fine to me viewing it from my very old Dell with a small monitor, and from my son’s laptop. My old Dell died and now when I view my site from a larger screen the header is to the left and the top nav bar and content is centered. I used code I found on a forum:

function.php

// This will create your widget area
function my_widgets_init() {
    register_sidebar(array(
       	'name' => 'Header Aside',
       	'id' => 'header-aside',
       	'before_widget' => '<li id="%1$s" class="widgetcontainer %2$s">',
       	'after_widget' => "",
		'before_title' => "<h3 class=\"widgettitle\">",
		'after_title' => "</h3>\n",
    ));

}
add_action( 'init', 'my_widgets_init' );

// adding the widget area to your child theme
function my_header_widgets() {
if ( function_exists('dynamic_sidebar') && is_sidebar_active('header-aside') ) {
    echo '<div id="header-aside" class="aside">'. "\n" . '<ul class="xoxo">' . "\n";
    dynamic_sidebar('header-aside');
    echo '' . "\n" . '</div><!-- #header-aside .aside -->'. "\n";
    echo "\n" . '</div><!-- #header-box -->'. "\n";
}
}
add_action('thematic_header', 'my_header_widgets', 8);

function remove_branding() {
		remove_action('thematic_header','thematic_brandingopen',1);
}
add_action('init', 'remove_branding');

function my_brandingopen() { ?>
	<div id="header_box">
    	<div id="branding">
<?php }
add_action('thematic_header','my_brandingopen',1);

style.css

#header_box {
	clear: both;
	margin: 30 auto;
	overflow: hidden;
	position: relative;
	width: 950px;
}

/* Moves blog name & description to the left */
#branding {
  float: left;
  width: 320px;
  margin: 0 0 0 36px;
}

/* Moves the new widgetized area to the right and levels it with #branding */
#header-aside {
  float: right;
  width: 347px;
  padding: 64px 0 20px;
}
/* This will clear the floats and keeps the access bottom line
from jumping into the air */
#access {
  clear: both;
}

#branding {
padding: 64px 0 20px;
}

[review http://codex.wordpress.org/Forum_Welcome#Posting_Code ]

Thank you for your help