HTML :
<body>
<header>
<div>
</div>
</header>
</body>
CSS :
body { width : 1000px ; }
header { width : 100% ; }
If these codes are implemented,
The header's width should be the same as the body's width.
However, it didn't work as expected.
Check out the code here: http://jsfiddle.net/o3omng/q4xewdew/
In the provided code, the .header's width is larger than the body's width.
Avoid simply adjusting the CSS like ".header { width : 1000px ; }"
since I am creating a responsive website. Please use percentages instead.