CSS Floating div inside another div

[beight]

i have a div that floats to left and another one that floats to rightthe main main div that including the floating div does not reach the bottom of the pageand the code example is:\[code\]<div style=" width: 900px; height:auto; margin:5px auto; background:#666; "> <div style="float:left;"> Some content! Some content! Some content! </div> <div style="float:right;"> Some content! Some content! Some content! </div></div>\[/code\]what is problem?