jquery - How to set fixed position to DIV into the page -

i have css box-model this:

using jquery (when button cliecked) resize main content div, footer doesn't maintain position @ bottom of screen:

i try set position: fixed footer div, doesn't scroll page.

i know if there way position footer regardless of content

use css achieve this

.my_footer {     position: fixed;     bottom: 0;     left: 0;     right: 0;     height: 100px; }