First of all, you shouldn't be changing anything in the classic folders. You should be creating your own template by copying the files you want to modify to a folder you create and making your changes there. If you use the files in the classic folders, you'll either lose all your changes with the next upgrade/update or have to spend a very long time comparing files to preserve your work.
In includes/languages/english/classic/header.php, find
Code:
define('HEADER_SALES_TEXT', '<h1>Sales Message Goes Here</h1>');
change it to
Code:
define('HEADER_SALES_TEXT', '');
Save it to includes/languages/english/YOUR_TEMPLATE/header.php (where YOUR_TEMPLATE is the name of your custom template).
In the stylesheet, change the line in green to change the green in the line in the sideboxes. Again, you should be saving the changed file to your own custom template folder.
Code:
.leftBoxContainer, .rightBoxContainer {
margin: 0em;
border: 1px solid #9a9a9a;
border-bottom: 5px solid #336633;
margin-top: 1.5em;
}