[css] CSS How to set div height 100% minus nPx

I haven't seen anything like this posted yet, but I thought I'd put it out there.

<div class="main">
<header>Header</header>
<div class="content">Content</div>

Then CSS:

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

.main {
    height: 100%;
    padding-top: 50px;
    box-sizing: border-box;
}

header {
    height: 50px;
    margin-top: -50px;
    width: 100%;
    background-color: #5078a5;
}

.content {
    height: 100%;
    background-color: #999999;
}

Here is a working jsfiddle

Note: I have no idea what the browser compatability is for this. I was just playing around with alternate solutions and this seemed to work well.