Basically any property in a HTML tag that isn't 'id', 'class' or sometimes 'visible' should go in the CSS.

Try putting the following in your CSS file:
Code:
#sidebar 
{

float:right;
}

#content
{

float:left;
width:85%;
}
'id' tags in the HTML start with a # in the CSS, while 'class' tags in the HTML start with '.'