How to fill 100% of remaining height?

You should be able to do this if you add in a div (#header below) to wrap your contents of 1.

  1. If you float #header, the content from #someid will be forced to flow around it.

  2. Next, you set #header's width to 100%. This will make it expand to fill the width of the containing div, #full. This will effectively push all of #someid's content below #header since there is no room to flow around the sides anymore.

  3. Finally, set #someid's height to 100%, this will make it the same height as #full.

JSFiddle

HTML

<div id="full">
    <div id="header">Contents of 1</div>
    <div id="someid">Contents of 2</div>
</div>

CSS

html, body, #full, #someid {
  height: 100%;
}

#header {
  float: left;
  width: 100%;
}

Update

I think it's worth mentioning that flexbox is well supported across modern browsers today. The CSS could be altered have #full become a flex container, and #someid should set it's flex grow to a value greater than 0.

html, body, #full {
  height: 100%;
}

#full {
  display: flex;
  flex-direction: column;
}

#someid {
  flex-grow: 1;
}

To get a div to 100% height on a page, you will need to set each object on the hierarchy above the div to 100% as well. for instance:

html { height:100%; }
body { height:100%; }
#full { height: 100%; }
#someid { height: 100%; }

Although I cannot fully understand your question, I'm assuming this is what you mean.

This is the example I am working from:

<html style="height:100%">
    <body style="height:100%">
        <div style="height:100%; width: 300px;">
            <div style="height:100%; background:blue;">

            </div>
        </div>
    </body>
</html>

Style is just a replacement for the CSS which I haven't externalised.


    html,
    body {
        height: 100%;
    }

    .parent {
        display: flex;
        flex-flow:column;
        height: 100%;
        background: white;
    }

    .child-top {
        flex: 0 1 auto;
        background: pink;
    }

    .child-bottom {
        flex: 1 1 auto;
        background: green;
    }
    <div class="parent">
        <div class="child-top">
          This child has just a bit of content
        </div>
        <div class="child-bottom">
          And this one fills the rest
        </div>
    </div>