<div id="fixed">Sidebar</div>
<div id="fluid">Content</div>
#fixed, #fluid{
padding:20px;
margin-left:2px;
margin-right:2px;
}
#fixed {
float:left;
width:150px;
background-color:#ccc;
}
#fluid {
overflow:hidden;/*没有此属性的话margin会失效*/
background-color:#999999;
}
http://jsfiddle.net/hhcncku5/