html {
  height: 100%;
}

body{
  position: relative;
  min-height: 100%;
}

body::before {
  content: "";
  position: absolute;
  top: 0; 
  left: 0;
  z-index: -1;
  width: 100%; 
  height: 100%;
  background: url('img/background.png') no-repeat ;
  filter: brightness(90%);
  background-size: cover;
}