SCSS

HTML

<div class="window">

    <div class="rectangle">


    </div>

</div>

SCSS

.window{
    .rectangle{
        position: absolute;
        bottom: 0px;
        right: 0px;
        border: solid 1px #4a4a4a;
        width: 20vw;
        height: 20vw;
        min-width: 200px;
        min-height: 200px;
    }
}

$mw: 500px !default;
@media screen and (max-width: ($mw)) {
  .window{
    .rectangle{
      left: calc(#{$mw} - 20vw);
    }
  }
}

$mh: 500px !default;
@media screen and (max-height: ($mh)) {
  .window {
    .rectangle {
      top: calc(#{$mh} - 20vw);
    }
  }
}