<header>

Sample HEADER External Cascading Stylesheet Code:
header {background-color:#369; color:white; font-size:24px; text-align:center}

Or for a HEADER BANNER IMAGE:
header {background-image:url('images/banner.jpg');
background-repeat:no-repeat; background-size:cover;
background-position:center center; position:relative;}

<main>

Simple Cascading Stylesheet and Nav Demo

This is a simple HTML5 semantic struture demo. The main content of the body is in the <main> element. It includes one <h1> tag and several <p> tags.

Right-click to View Source and see the simple semantic elements and <div> stucture.

Right-click to View Source, then click the line 11 link CascadingStylesheetDemo.css to open and view the External Cascading Stylesheet. It defines the HTML5 semantic stucture elements: header, nav, main and footer. It also defines the #wrapper id for the wrapper div. And it gives customized attributes to tags like <h1>, <p>, <img>, <hr>...

Also see: 7 Simple Responsive HTML Templates