body {
    margin: 0;
}


header {
    height: 80px;
    background-color: antiquewhite;
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    z-index: 1;
    transition: all 1s;
}

.inactive {
   
    top: -100px;
}

.active  {
  top: 0;
    background-color: darkblue;
    color: #fff;
}

main {
    height: 200vh;
}