Best way to style a default HTML 5 page?

What would be the best way to style a HTML 5 website (to also function in IE6)?

<header>
  开发者_Python百科  [ Header ]
</header>

<section>

    <article>
        Lorem ipsum dolor sit amet, consectetur adipiscing elit. Praesent varius ultricies nibh faucibus tempor. Aliquam erat volutpat. Vestibulum ante ipsum primis in faucibus orci luctus et ultrices posuere cubilia Curae; Praesent hendrerit nunc vitae nisl accumsan dictum. Vestibulum ante ipsum primis in faucibus orci luctus et ultrices posuere cubilia Curae; Integer convallis lobortis turpis posuere semper. Proin ligula mi, hendrerit sit amet feugiat eu, dapibus sed ante. Donec lacinia aliquam felis at gravida. Praesent varius lectus enim. Nulla vehicula, odio id feugiat ornare, nibh urna elementum arcu, ut suscipit odio velit vel augue. Maecenas enim dolor, tincidunt a luctus ornare, viverra ut lorem. Suspendisse imperdiet est id mi pulvinar quis interdum felis vehicula.
    </article>

    <aside>
        [ Aside ]
    </aside>

</section>

<footer>
    [ Footer ]
</footer>

CSS

header {
    display:block;
    clear:both;
    background-color:red;
    height:43px;
}

section article {
    display:block;
    float:left;
    width:800px;
    background-color:green;
}

section aside { 
    display:block;
    width:180px;
    background-color:lime;
}

footer {
    display:block;
    clear:both;
    background-color:blue;
    height:43px;
}

My real question, must I now add after the tag?

Everything you need to know is at http://html5boilerplate.com/

Remember to add

<!--[if lt IE 9]>
<script src="http://html5shim.googlecode.com/svn/trunk/html5.js"></script>
<![endif]-->

To your head to ensure that IE can style these elements.