Two points that may help:
There is no reason I know of to use a full http filepath for the background image. Using
background-image: url(../images/dropsh.gif);
will get the desired results, and allow your code to be portable to a test/development environment as well.
It may be necessary for proper function to do the divs in the same way I did them: #mainWrapper with #mainWrapperRight inside it.
Give #mainWrapper the desired width and margin: auto;
Give #mainWrapperRight width: 100%;
Code:
#mainWrapper {
background-color: #ffffff;
text-align: left;
width: 850px;
margin: auto;
vertical-align: top;
}
#mainWrapperRight {
width: 100%;
background-image: url(../images/dropsh.gif);
background-position: top right;
background-repeat: repeat-y;
padding-right:7px; /*or whatever the shadow width is*/
}
PHP Code:
?>
<div id="mainWrapper">
<div id="mainWrapperRight">
<?php
/**
* prepares and displays header output
*
*/
require($template->get_template_dir('tpl_header.php',DIR_WS_TEMPLATE , $current_page_base,'common'). '/tpl_header.php');?>
and don't forget to add an extra </div> at the end of the file to properly close the new div.