Customize header CSS

Dear all,
I want to customize the header in the advantage theme. It should be a super easy one to make, just a white background and one image in the center. I wanted to follow this tutorial to do it http://codex.ww.wp.xz.cn/Designing_Headers,

But this directs me to the CSS Stylesheet, which says:
—————————————————————– */
/* Surprised to see empty stylesheet? Please note that Advantage
* uses minified verion of stylesheet. The source is located on
* dev/advantage.css. You may use one of the follow options:
* 1. Save Custom CSS in Theme Options
* 2. Create a Child Theme. Advantage will include Child Theme’s
* style.css automatically.
—————————————————————– */

So, in essence, if I would put in the following code in the custom CSS Stylesheet, would this then automatically overwrite the ‘usual’ header code and allow me to insert my ‘logo’ header image?

Thanks in advance!

#header {
  background: url("<?php bloginfo('stylesheet_directory'); ?>/images/logo.jpg")
  no-repeat bottom center; }
#headerimg  {
  margin: 7px 9px 0;
  height: 200px;
  width: 740px; }