Make absolute positioned div expand parent div hei

Question

As you can see in the CSS below, I want child2 to position itself before child1. This is because the site I'm currently developing should also work on mobile devices, on which the child2 should be at the bottom, as it contains the navigation which I want below the content on the mobile devices. - Why not 2 masterpages? This is the only 2 divs which are repositioned in the entire HTML, so 2 masterpages for this minor change is an overkill.

HTML:

<div id="parent">
    <div class="child1"></div>
    <div class="child2"></div>
</div>

CSS:

parent { position: relative; width: 100%; }
child1 { width: auto; margin-left: 160px; }
child2 { width: 145px; position: absolute; top: 0px; bottom: 0px; }

child2 has dynamic height, as different subsites could have more or less navigation items.

I know that absolute positioned elements are removed from the flow, thus ignored by other elements.
I tried setting overflow:hidden; on the parent div, but that didn't help, neither does the clearfix.

My last resort will be javascript to reposition the two divs accordingly, but for now I'll try and see if there exist a non-javascript way of doing this.

Answer 1

There is a quite simple way to solve this.

You just have to duplicate the content of child1 and child2 in relative divs with display:none in parent div. Say child1_1 and child2_2. Put child2_2 on top and child1_1 at the bottom.

When your jquery (or whatever) calls the absolute div, just set the according relative div (child1_1 or child2_2) with display:block AND visibility:hidden. The relative child will still be invisible but will make parent's div higher.

Answer 2

There's a very simple hack that fixes this issue

Here's a codesandbox that illustrates the solution: https://codesandbox.io/s/00w06z1n5l

HTML

<div id="parent">
  <div class="hack">
   <div class="child">
   </div>
  </div>
</div>

CSS

.parent { position: relative; width: 100%; }
.hack { position: absolute; left:0; right:0; top:0;}
.child { position: absolute; left: 0; right: 0; bottom:0; }

you can play with the positioning of the hack div to affect where the child positions itself.

Here's a snippet:

html {
  font-family: sans-serif;
  text-align: center;
}

.container {
  border: 2px solid gray;
  height: 400px;
  display: flex;
  flex-direction: column;
}

.stuff-the-middle {
  background: papayawhip
    url("https://camo.githubusercontent.com/6609e7239d46222bbcbd846155351a8ce06eb11f/687474703a2f2f692e696d6775722e636f6d2f4e577a764a6d6d2e706e67");
  flex: 1;
}

.parent {
  background: palevioletred;
  position: relative;
}

.hack {
  position: absolute;
  left: 0;
  top:0;
  right: 0;
}
.child {
  height: 40px;
  background: rgba(0, 0, 0, 0.5);
  position: absolute;
  bottom: 0;
  left: 0;
  right: 0;
}

    <div class="container">
      <div class="stuff-the-middle">
        I have stuff annoyingly in th emiddle
      </div>
      <div class="parent">
        <div class="hack">
          <div class="child">
            I'm inside of my parent but absolutely on top
          </div>
        </div>
        I'm the parent
        <br /> You can modify my height
        <br /> and my child is always on top
        <br /> absolutely on top
        <br /> try removing this text
      </div>
    </div>

Answer 3

Feeela is right but you can get a parent div contracting/expanding to a child element if you reverse your div positioning like this:

.parent{
    postion: absolute;
    /* position it in the browser using the `left`, `top` and `margin` 
       attributes */
}

.child{
    position: relative;
    height: 100%;
    width: 100%;

    overflow: hidden;
    /* to pad or move it around using `left` and `top` inside the parent */
}

This should work for you.

Answer 4

There is a better way to do this now. You can use the bottom property.

    .my-element {
      position: absolute;
      bottom: 30px;
    }

Answer 5

I had a similar problem. To solve this (instead of calculate the iframe's height using the body, document or window) I created a div that wraps the whole page content (a div with an id="page" for example) and then I used its height.

Answer 6

I came up with another solution, which I don't love but gets the job done.

Basically duplicate the child elements in such a way that the duplicates are not visible.

<div id="parent">
    <div class="width-calc">
        <div class="child1"></div>
        <div class="child2"></div>
    </div>

    <div class="child1"></div>
    <div class="child2"></div>
</div>

CSS:

.width-calc {
    height: 0;
    overflow: hidden;
}

If those child elements contain little markup, then the impact will be small.