Edit in JSFiddle

<html>
    <head><title>mark tag in html5</title>
    </head>
    <body>
        <header>
            <b>jQuery</b><br />
            <span style="margin-left:210px;">jQuery is amazing !!!</span>
        </header>
        <br /><br />
        <p>The header section represents a header section in the document.
The HTML header tag represents a group of introductory or navigational aids.
The header tag cannot be placed within a footer, address or another header element.
The header tag is supported in Internet Explorer 9, Firefox, Opera, Chrome, and Safari. IE8 and earlier versions does not support header tag.</p>
    </body>
</html>

b
{
    margin-left:240px;
    font-size:20px;
    font-weight:bolder;
}