http://www.w3schools.com/css/css_boxmodel.asp
when you increase the padding on an element in the styles, you need to decrease the width accordingly.
i see that you have quite large padding in style.css, here:
#content {
float:left;
padding:10px 62px 10px 68px;
width:570px;
}
and a bit of padding on the sidebar:
#sidebar1 {
float: left;
width: 270px;
padding: 5px 20px;
font-size:0.9em;
margin:25px;
}
possibly try to reduce the width or padding in the #content style, until the sidebar pops back up to the side.