Margini in Home Page

If your browser is simply larger that content height it will just display empty space. You can maybe but some background color for body because white in your case does not look good.

BODY{
background:....
}

put it at end of template_css.css

There's no difference. Simply, the amount of content is different. This empty area could be smaller or larger depending of the user's screen resolution. I don't think you should care about this.