Position absolute div in center of screen view

Question

Use the following CSS:

.centered {
  position: fixed;
  top: 50%;
  left: 50%;
  /* bring your own prefixes */
  transform: translate(-50%, -50%);
}

Change position:absolute to position: fixed and you should be good to go!

When you say position - absolute, the reference div is the parent div that has a position - relative. However if you say position -fixed, the reference is the browser's window. which is wat you want in your case.

In the case of IE6 i guess you have to use CSS Expression

If you don't want to change your element's position to fixed, here is a solution with keeping your element absolut.

Since CSS's calc() is supported by all browsers now, here a solution using calc().

#main {
    width: 140px;
    height:100px;
    border: 1px solid Black;
    text-align: left;
    position: absolute;
    top: calc(50vh - (/* height */100px / 2));
    left: calc(50vw - (/* width */140px / 2)); 
}

A bit more complex way is to use multiple outer boxes. This method works well with or without hard coded width/height of the middle box (background colors added just to show what each box does):

/* content of this box will be centered horizontally */
.boxH
{
  background-color: rgba(0, 127, 255, 0.2);
  width: 100%;
  height: 100%;
  position: absolute;
  top: 0;
  left: 0;
  display: flex;
  flex-direction: column;
  align-items: center;
}

/* content of this box will be centered vertically */
.boxV
{
  background-color: rgba(255, 0, 0, 0.2);
  height: 100%;
  display: flex;
  flex-direction: row;
  align-items: center;
}

/* content of this box will be centered horizontally and vertically */
 .boxM
{
  background-color: lightblue;
  padding: 3em;
}

<div>
  some text in the background
</div>
<div class="boxH">
  <div class="boxV">
    <div class="boxM">
      this div is in the middle
    </div>
  </div>
</div>

https://jsfiddle.net/vanowm/7cj1775e/

If you want display div in the middle regardless of the scroll position, then change position to fixed