Frisco Theme Sidebar of width 300

I want a sidebar of width 300 so that i can easily place ads of size 300 x 250 on all the blog pages and buddypress pages.

I created a new custom.css file and placed it in the frisco theme directory and enabled custom css in the theme options. I used the following code but the sidebar is not placed properly on the blog and buddypress pages. In the blog pages, the sidebar comes over the post and in the buddypress pages, the sidebar starts after the page ends.

I tried solving this using firebug in firefox but i was not able to solve this problem. Could you please help me with this problem?

Thanks in advance

The code which i used :

div#sidebar {
margin-left: -302px;
width: 300px;
}

div#content .padder {
margin-right: 301px;
}

http://wordpress.org/extend/themes/frisco-for-buddypress/