Change width and position

i tried doing the same thing but failed.

I made the following entries into local.css

/* $Id: local_sample.css,v 1.1.2.2 2008/12/15 21:02:34 jwolf Exp $ */

/****************************/
/* LOCAL CSS */
/****************************/

/* Put your custom css and css overrides in this file and */
/* rename it local.css. By restricting your css changes */
/* to local.css, your changes will not be overwritten when */
/* upgrading to a new version of this theme. */

/* Steps to activate local.css: */
/* 1. Add your custom css to this file */
/* 2. Rename this file to local.css */
/* 3. Uncomment (remove leading semicolon from ) the */
/* following line in your theme's .info file: */
/* ;stylesheets[all][] = local.css */
/* 4. Clear cached data at admin/settings/performance */
#legal-notice {
display: none;
}

#header {
background-color: inherit;
margin: 0 auto;
padding: 0;
/* width: 960px; */
width: 100%;
}

#primary-menu-wrapper {
margin: 0 auto;
position: relative;
/* width: 960px; */
width: 95%;
z-index: 5; /* fixes IE z-index bug */
}

#preface-wrapper {
color: #fff;
font-family: Myriad Pro, Myriad Web Pro Regular, Lucida Grande, Geneva, Trebuchet MS, sans-serif;
font-size: 1.5em;
margin: 0 auto;
padding: 10px 0 8px 0;
/* width: 960px; */
width: 100%;
}

#main {
margin: 0 auto;
/* width: 960px; */
width: 100%;
}

#postscript-wrapper {
clear: both;
margin: 0 auto;
/* width: 960px; */
width: 100%;
}

#footer {
border-bottom: 1px solid #D6DDB9;
border-top: 1px solid #D6DDB9;
clear: both;
display: block;
font-size: 0.9em;
margin: auto 0;
overflow: hidden;
padding: 10px 0;
text-align: center;
/* width: 960px; */
width: 100%;
}

Anand