As you may have already figured the stacking order means that your content ( or more specifcally, the MARGIN from your content is on top of your left column)...
I think you tried to fix this by using, z-index. What you forgot was that you need to give something a position:(something other than "static" which is default) before you can use z-index. in this case the best thing to use is position:relative;
margin:0 250px 0 250px;
border:2px solid green;
<font color='"Red"'> position:relative;</font>