<div class="filler">filler</div>
  <div class="container">
  <div class="offset">
    <div class="fixed"><div class="content"></div></div>
  </div>
</div>

.filler {
    height: 100px;
    background: yellow;
}
.offset {
    height: 100px;
    width:100px;
    background:blue;
    float:right;
    position:static;
}
.container {
    width:200px;
}
.fixed {
    position: fixed;
    bottom:10vh;
    left:10vw;
    max-height: 80vh;
    opacity: 0.5;
    z-index: 120;
    margin: 0px;
    overflow-y: scroll;
    width: 80vw;
    background: red;
       -webkit-transition: all 0.4s linear;
    -moz-transition: all 0.4s linear;
    -o-transition: all 0.4s linear;
    -ms-transition: all 0.4s linear;
    transition: all 0.4s linear;
}

.content {
    height: 1000px;
}