#chat-wrapper {
  float: right;
}
html, body { 
 height: 100%; width: 100%; 
 margin: 0px;
}
#video-wrapper { height: 100%; } 
@media screen and (max-width: 800px) {
  #chat-wrapper {
    width: 100%;
    height: 50%;
  } 
  #video-wrapper { 
    width: 100%;
    height: 50%;
  }
}

@media screen and (min-width: 800px) {
  #chat-wrapper  {
    width: 30%;
  } 
  #video-wrapper { 
    width: 70%;
  }
}