[рони]

dupre,

body:after{
opacity: 0;
content: "";
}

body.open:after{
  content: "";
  background-color: #A9A9A9;
  opacity: .3;
  left:250px;
  right: 0;
  top: 0;
  bottom: 0;
  position: fixed;
  transition: all 0.3s 0.3s;
}