How do I change the white background color or Corporate theme?

Which file should I modify? I tried to modify /bp-corporate/_inc/css/custom.css line #62 background but there was no effect:

body {
font-family: "Lucida Grande", Verdana, Tahoma, "Trebuchet MS";
font-size: 100%;
color: #444;
background: f9f9f9;
margin: 0px;
padding: 0px;
}

Any suggestion? Thx!