Body element is not always ignored (particularly in Outlook), however you should also pair it with a full width table as a fallback. This also makes a good method to have the forwarding background color remain white, while your html area background remains something else.
Here is a basic setup with this in mind:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"><title></title>
<style type="text/css">
/* Client-specific Styles */
#outlook a {padding:0;}
body{width:100% !important; -webkit-text-size-adjust:100%; -ms-text-size-adjust:100%; margin:0; padding:0;} /* force default font sizes */
.ExternalClass {width:100%;} .ExternalClass, .ExternalClass p, .ExternalClass span, .ExternalClass font, .ExternalClass td, .ExternalClass div {line-height: 100%;} /* Hotmail */
a:active, a:visited, a[href^="tel"], a[href^="sms"] { text-decoration: none; color: #000001 !important; pointer-events: auto; cursor: default;}
table td {border-collapse: collapse;}
</style>
</head>
<body leftmargin="0" topmargin="0" marginwidth="0" marginheight="0" style="margin: 0px; padding: 0px; background-color: #FFFFFF;" bgcolor="#FFFFFF"><table bgcolor="#252525" width="100%" border="0" align="center" cellpadding="0" cellspacing="0"><tr><td><table width="600" border="0" align="center" cellpadding="0" cellspacing="0"><tr><td valign="top" style="padding-top:30px; padding-bottom:30px;">
<table width="100%" border="0" cellpadding="0" cellspacing="0">
<tr>
<td bgcolor="#FFFFFF" style="padding:30px;">
Content here
</td>
</tr>
</table>
</td></tr></table></td></tr></table></body></html>
On a side note, if you want a backgorund image, there are 2 methods in html email. See this answer for more details.