Untitled

<div class="container">

  <div class="dontainer">

    :D

  </div>

</div>

html, body {

  margin: 0;

}

.container {

  position: absolute;

  top: 0;

  bottom: 50%;

  width: 50%;

  left: 25%;

  outline: 1px solid red;

/* Uncomment for some mild awesomeness: */

/* transition: bottom 0.5s ease-out; */

}

.dontainer {

  position: absolute;

  bottom: 0;

  outline: 1px solid lime;

}

function doTheThing() {

  var ce = document.querySelector(".container");

  ce.style.bottom = ce.style.bottom === "50%" ? "0%" : "50%";

}

setInterval(doTheThing, 1000);