Website CSS cross browser website alignment issue help?

Hi guys i have developed a webpage .which is not compatible in diff browsers.The alignment is changing in different browser.How to fix this CSS issue.
I tried giving prefixes like shown below for the margin but still no effect
#site_content
{ width: 858px;
  overflow: hidden;
  -moz-margin: 0 0 0 400px;
  margin: 0 0 0 235px;
  padding: 10px 20px 20px 20px;
  background: #ECEBEB ;
  border: 15px solid #222020;}
How to make the margin conditional for diff browsers?
help me out guys
Answer #1
for safari add this line to your css
-webkit-margin-start-margin: 0 0 0 400px;
hope this helps