You need to use an HTML shiv so older versions can tell what the new HTML5 tags are. For the use of CSS3, you need backup images or something for older versions to fall back on.
HTML5 Shiv IS A MUST FOR OLDER BROWSERS! This is why your site looks crazy. Older browsers don’t know what a nav or header tag is so it will not display any of those styles.
6
solved Built a site in HTML5 and CSS3 and now can’t be viewed on Internet Explorer [closed]