Relative div height

add this to you CSS:

html, body
{
    height: 100%;
}

working Fiddle

when you say to wrap to be 100%, 100% of what? of its parent (body), so his parent has to have some height.

and the same goes for body, his parent his html. html parent his the viewport.. so, by setting them both to 100%, wrap can also have a percentage height.

also: the elements have some default padding/margin, that causes them to span a little more then the height you applied to them. (causing a scroll bar) you can use

*
{
    padding: 0;
    margin: 0;
}

to disable that.

Look at That Fiddle

When you set a percentage height on an element who's parent elements don't have heights set, the parent elements have a default

height: auto;

You are asking the browser to calculate a height from an undefined value. Since that would equal a null-value, the result is that the browser does nothing with the height of child elements.

Besides using a JavaScript solution you could use this deadly easy table method:

#parent3 {
    display: table;
    width: 100%;
}

#parent3 .between {
    display: table-row;
}

#parent3 .child {
    display: table-cell;
}

Preview on http://jsbin.com/IkEqAfi/1

• Example 1: Not working
• Example 2: Fix height
• Example 3: Table method

But: Bare in mind, that the table method only works properly in all modern Browsers and the Internet Explorer 8 and higher. As Fallback you could use JavaScript.

add this to your css:

html, body{height: 100%}

and change the max-height of #block12 to height

Explanation:

Basically #wrap was 100% height (relative measure) but when you use relative measures it looks for its parent element's measure, and it's normally undefined because it's also relative. The only element(s) being able to use a relative heights are body and or html themselves depending on the browser, the rest of the elements need a parent element with absolute height.

But be careful, it's tricky playing around with relative heights, you have to calculate properly your header's height so you can substract it from the other element's percentages.