Adjust the width of the div to the width of the site - css

Question

I need the center div div#b to fill out the gab between div#a and div#c.
<div id="a">
<span>Div1</span>
</div>
<div id="b">
<span>Div2</span>
</div>
<div id="c">
<span>Div3</span>
</div>
I tried to do this by placing width: 100% on div#b but without luck.
div
{
border:1px solid red;
}
div#a
{
float:left;
width:50px;
}
div#b
{
float:left;
width:100%; ?? <!-- Doesn't work!!! -->
}
div#c
{
float:right;
width:50px;
}
How can I get div#b to expand from div#a to div#c?
There can be no line breaks.

Answer 1

CSS3
You can implement this dynamic behavior using the CSS3 Flexible Box Layout Module:
<style type="text/css">
div.Container
{
width: 100%;
display: box;
display: -moz-box;
display: -ms-box;
display: -webkit-box;
}
div.B
{
background: magenta;
box-flex: 1;
-moz-box-flex: 1;
-ms-box-flex: 1;
-webkit-box-flex: 1;
}
</style>
<div class="Container">
<div style="width: 50px; background: cyan;">
A
</div>
<div class="B">
B
</div>
<div style="width: 50px; background: yellow;">
C
</div>
</div>
A new version of FireFox, a new version of Google Chrome, Internet Explorer 10 and a new version of Safari supports CSS3 flexible box layout. Internet Explorer 9 and Opera is lacking support at the moment.
I also want to mention this new way to do it in FireFox:
<div style="float: left; width: 50px; background: cyan;">
A
</div>
<div style="float: left; width: -moz-calc(100% - 100px); background: magenta;">
B
</div>
<div style="float: left; width: 50px; background: yellow;">
C
</div>
FireFox is the only browser that support the calc function at the moment.
CSS2
Here is the old way to do it:
<div style="padding-left: 100px;">
<div style="float: left; width: 50px; margin-left: -100px; background: cyan;">
A
</div>
<div style="float: left; width: 100%; margin-left: -50px; background: magenta;">
B
</div>
<div style="float: left; width: 50px; background: yellow;">
C
</div>
</div>
A width of 100% inside the container div is the width of the container minus the 100px left padding. Then there is room for the left and right 50px div elements. Then you have to position them using some negative margin and floating.
Feature detection
Use feature detection with Modernizr. Then you can use CSS2 for browsers that lack support for CSS3 flexbox.
If you do .NET development you can download Modernizr with NuGet.

Answer 2

I've hit similar problems myself. The problem here is "width: 100%" will basically inherit the width of the parent container.
The other problem is the float. When you ask div#b to float to the left alongside div#a, you can't use the fancy margin trick to force div#b to stay out of the way of div#a. (In other words, margin can be used to keep div#b from entering and interfering with a certain amount of space on any of its sides.) However, with float, the margin is now not pushing div#b away from the edge of the page, but away from the edge of div#a.
OK, so the solution looks like this. Remove the float on div#b, and then apply left and right margins so div#b doesn't interfere with either side columns. Let div#b determine its own size (i.e. don't give it a "width"), so it will fit between the two floats. Lastly, shift div#b so that the floats occur before div#b is put in place, so that div#b is put between the floats.
Here's the new code:
<style type="text/css">
div
{
border:1px solid red;
}
div#a
{
float:left;
width:50px;
}
div#b
{
margin-left: 55px;
margin-right: 55px;
}
div#c
{
float:right;
width:50px;
}
</style>
<div id="a">
<span>Div1</span>
</div>
<div id="c">
<span>Div3</span>
</div>
<div id="b">
<span>Div2</span>
</div>
Determining margins is tricky. Borders aren't counted in the width calculation of an element, so a 50px-wide div with a 1px border is actually 52px-wide.

Answer 3

I have a feeling you won't like this answer, but the easiest way to do it is to remove float: left and any width from div#b, and then switch up the order of your divs, so both the sidebars are before your main content area. Here's the code:
HTML:
<div id="a">
<span>Div1</span>
</div>
<div id="c">
<span>Div3</span>
</div>
<div id="b">
<span>Div2</span>
</div>
CSS:
div
{
border:1px solid red;
}
div#a
{
float:left;
width:50px;
}
div#b
{
overflow: hidden;
/*margin: 0 60px;*/
}
div#c
{
float:right;
width:50px;
}
Note that I've applied overflow: hidden to the middle div - this will force it into columns (in most browsers). You could use the given margins instead, if you're not comfortable with a "magic" solution (there is a reasonable explanation for it, but I can never remember it off the top of my head).