Height 100% minus the top navigation - css

Question

I have a site that has a top navigation bar, a header, a sidebar and a content body next to the sidebar. The header, sidebar, and content body are positioned absolutely so that they don't move when you navigate to other pages that are using the same template. The sidebar and content body have scroll bars. The header and sidebar are always visible even with scrolling. This works great as shown in the demo. But suppose the top navigation changes height. Then the vertical alignment is off. Since this site is using a global top navigation that's used in other sites as well, the top navigation can change at any moment. When it does change, this layout will not be future proof. Is there a way to make this future proof?
What I have currently:
http://codepen.io/codingninja/pen/nKwox
body {
margin: 0;
padding: 0;
}
.content {
/*position: relative;*/
}
.top-nav {
background: #000;
height: 42px;
color: #fff;
}
.header{
position: absolute;
height: 100px;
width: 100%;
background: #ddd;
}
.sidebar {
position: absolute;
top: 142px;
left: 0;
bottom: 0;
background: #aaa;
overflow-y: auto;
overflow-x: hidden;
width: 100px;
}
.body {
position: absolute;
top: 142px;
right: 0;
left: 150px;
bottom: 0;
overflow-y: auto;
overflow-x: hidden;
}
What happens when the top nav changes height:
http://codepen.io/codingninja/pen/nICzK
.top-nav {
background: #000;
height: 100px;
color: #fff;
}

Answer 1

Do you mean this:
Css3 has a Calc() Function
Height: Calc( 100% - 100px )

Answer 2

Instead of absolutely positioning everything you can make use of display:table to achieve the layout you want. Using the following html
<div class="table">
<div id="top-nav" class="row">
<div class="cell">top-nav</div>
</div>
<div id="header" class="row">
<div class="cell">header</div>
</div>
<div id="content" class="row">
<div class="cell">
<div class="table">
<div id="side-bar" class="cell">
<div class="overflow">
sidebar
</div>
</div>
<div id="body-content" class="cell">
<div class="overflow">body-content</div>
</div>
</div>
</div>
</div>
</div>
And Css
html,
body,
.table {height:100%; padding:0; margin:0;}
.table {display:table; width:100%;}
.table .row {display:table-row;}
.table .cell {display:table-cell;}
#top-nav {height:42px;}
#header {height:100px;}
#content {height:100%;}
#side-bar {width:100px;}
.overflow {height:100%; overflow:auto;}
Example
You will notice that when your top nav grows, your main content area will shrink. You will also not get into a positioning / z-index nightmare

Answer 3

I found a solution that involves a line of javascript to set top to the calculated height based on the height of the top nav and the header.
$(".sidebar, .body").css('top', topnavheight+100);