You probably forget to style the new HTML5 elements as block level elements. By default, browsers treat any unknown element as an inline element ( display:inline ), which makes them difficult to execute.
Newer browsers are slowly treating the new HTML5 elements as stable, which means that they are starting to use the default style, for example display:block for the header element. But most browsers on the market today do not have these default styles for HTML5 elements, so you need to provide them.
To do this, you need a quick CSS example:
article, aside, details, figcaption, figure, footer, header, hgroup, menu, nav, section { display: block; }
Adding this CSS to your main.css should fix your design problem.
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