How to Position an Element Fixed Relative to Parent

Can I position an element fixed relative to parent?

Let me provide answers to both possible questions. Note that your existing title (and original post) ask a question different than what you seek in your edit and subsequent comment.

To position an element "fixed" relative to a parent element, you want position:absolute on the child element, and any position mode other than the default or static on your parent element.

For example:

#parentDiv { position:relative; }
#childDiv { position:absolute; left:50px; top:20px; }

This will position childDiv element 50 pixels left and 20 pixels down relative to parentDiv's position.

To position an element "fixed" relative to the window, you want position:fixed, and can use top:, left:, right:, and bottom: to position as you see fit.

For example:

#yourDiv { position:fixed; bottom:40px; right:40px; }

This will position yourDiv fixed relative to the web browser window, 40 pixels from the bottom edge and 40 pixels from the right edge.

Fixed position but relative to container

Short answer: no. (It is now possible with CSS transform. See the edit below)

Long answer: The problem with using "fixed" positioning is that it takes the element out of flow. thus it can't be re-positioned relative to its parent because it's as if it didn't have one. If, however, the container is of a fixed, known width, you can use something like:

#fixedContainer {
  position: fixed;
  width: 600px;
  height: 200px;
  left: 50%;
  top: 0%;
  margin-left: -300px; /*half the width*/
}

http://jsfiddle.net/HFjU6/1/

Edit (03/2015):

This is outdated information. It is now possible to center content of an dynamic size (horizontally and vertically) with the help of the magic of CSS3 transform. The same principle applies, but instead of using margin to offset your container, you can use translateX(-50%). This doesn't work with the above margin trick because you don't know how much to offset it unless the width is fixed and you can't use relative values (like 50%) because it will be relative to the parent and not the element it's applied to. transform behaves differently. Its values are relative to the element they are applied to. Thus, 50% for transform means half the width of the element, while 50% for margin is half of the parent's width. This is an IE9+ solution

Using similar code to the above example, I recreated the same scenario using completely dynamic width and height:

.fixedContainer {
    background-color:#ddd;
    position: fixed;
    padding: 2em;
    left: 50%;
    top: 0%;
    transform: translateX(-50%);
}

If you want it to be centered, you can do that too:

.fixedContainer {
    background-color:#ddd;
    position: fixed;
    padding: 2em;
    left: 50%;
    top: 50%;
    transform: translate(-50%, -50%);
}

Demos:

jsFiddle: Centered horizontally only

jsFiddle: Centered both horizontally and vertically

Original credit goes to user aaronk6 for pointing it out to me in this answer

Fixed position relative to parent container

The problem here is with the -webkit-transform.

Chrome cannot render position:fixed on elements under a transformation.

Read here

You can try removing the transform from .absolute div and set a margin-left to the .fixed div after calculating it's parents width. in your case it's 40px.

Example:

.absolute{
  height:60px;
  width: 60px;
  position: absolute;
  top:0;
  right:0;
  background: #ccc;
  /* -webkit-transform: translateZ(0);  */
}

.fixed{
  height:20px;
  width: 20px;
  background: red;
  position: fixed;
  margin-left: 40px;
}

JSFiddle DEMO

Fixed element positioning relative to its parent

'normally' position fixed fixes relative to the viewport.

But there are exceptions. See MDN

The element is removed from the normal document flow, and no space is created for the element in the page layout. It is positioned relative to the initial containing block established by the viewport, except when one of its ancestors has a transform, perspective, or filter property set to something other than none (see the CSS Transforms Spec), in which case that ancestor behaves as the containing block. (Note that there are browser inconsistencies with perspective and filter contributing to containing block formation.) Its final position is determined by the values of top, right, bottom, and left.

Here's a simple example:

body {}

.parent {
  position: relative;
  margin: 100px;
  transform: scale(1);
  width: 50vw;
  height: 10vw;
  background: black;
  rfilter: blur(1);
}

.child {
  position: fixed;
  top: 0px;
  left: 0px;
  width: 100px;
  height: 100px;
  background-color: blue;
}

<body>
  <div class="parent">
    <div class="child"></div>
  </div>
</body>