Responsive Chat app using css media queries

The problem i had with this project was the positioning, not on the chat app but the big backgrounds, most especially the one at the bottom, i tried to position to the bottom right using "position:absolute;" "bottom: -500px;", "right: -200px;", instead of pushing it down and right the viewport, it just increased the size of the viewport i.e increasing the height and the width.i'd really appreciate it if you can tell me what i should have done