CSS - 100% Height with Header and Footer

Question

I am trying to design a page with a header, a main div that stretches to 100% of the vertical landscape (minus header and footer) and a footer. Like this pic:

I can get the header and main div to work. Like this:

    <div id="wrapper">

        <div class="header_div">HEADER</div>
        <div class="main_div">MAIN</div>
        <div class="footer_div">FOOTER</div>

    </div>

With this CSS:

html {
    height: 100%;
 }

 body {
    margin: 0;
    padding: 0;
    height: 100%;
 }

.header_div{

    height: 40px;
    width: 100%;
    background-color: #000000;

}

.main_div{

    margin-bottom:40px;
    margin-top:40px;
    position:absolute;
    top:0px;
    left:0px;
    right:0px;
    bottom:0px;
    background-color: red;
}


.footer_div{

    position: relative;
    height: 40px;
    width: 100%;
    background-color: blue;
}

So the main div starts 40px off the top to account for the header and then stops 40px from the bottom to account for the footer. This works well but I cannot get the footer div to show below the main div. The way it is now with position: relative it's putting the footer on top of the main div. If I use position:absolute it puts it underneath the main div.

I am sure I am just doing this wrong because CSS is not my thing.

Any help on this would be great.

Thanks

Answer 1

Using CSS3 Flexbox:

/*QuickReset*/ * { margin: 0; box-sizing: border-box; }

body {  /* or any parent wrapper */
  display: flex;
  flex-direction: column;
  min-height: 100dvh;
}

main {
  flex: 1;
}

<header>HEADER</header>
<main>MAIN</main>
<footer>FOOTER</footer>

Answer 2

Use the css calc() function.

With this method, you don't have to define the position of the elements

Here is a demo

html:

<header>Header</header>
<main>Main</main>
<footer>Footer</footer>

css:

html, body { 
    height: 100%
}

body {
    color: #FFF;
    padding: 0;
    margin: 0;
}

header { 
    background-color: #000;
    height: 100px;    
}

main { 
    background-color: #AAA;
    height: calc(100% - 150px);    
}

footer { 
    background-color: #000;
    height: 50px;    
}

Answer 3

Here's a simple method. Try this jsfiddle: http://jsfiddle.net/PejHr/

HTML:

<div id="top"></div>
<div id="main">
    <div id="inner"></div>
</div>
<div id="bottom"></div>

CSS:

#main {
    width: 100%;
    height: 100%;
    position: absolute;
    left: 0px;
    top: 0px;
    padding: 50px 0px
}
#inner {
    width: 100%;
    height: 100%;
    background: #f0f;
}

#top, #bottom {
    width: 100%;
    height: 50px;
    background: #333;
    position: absolute;
    top: 0px;
    left: 0px;
}

#bottom {
    bottom: 0px;
}