Auto change the height of <div> as included content increase

[Bharat383]

hello friends.....
i am developing one project in which now i am on design mode. i have made index.html page in that one main_contnent <div> which contains these three sub <div>
1> left_content
2> middle_content
3> right_content

now the problem occured when the contents or text in any <div> from above mentioned the main_content <div> does not auto height.

in css i have code as min-height:400px;

i am attaching file which content index.html, style.css and related images.

[Bharat383]

if any one wanna to try then in <div class="left_con tent"> place some long height content or text.</div>

[Rabbit]

Please post the relevant CSS and HTML in the post.