If by chance you have control over the content then I would suggest discarding the use of iframe and code the form in the same page. The code below may or may not be more than you are use too in regards to writing web content and if so there are plenty of sites that can assist with learning about css. Of course if you are not able to change how content is done the following is of no use.
I had a page done and tweaked it to use an iframe then without an iframe. The legend style is setup for IE and if was used in a production environment would have a css style sheet to determine the agent (browser) to conditionally style the legend. Also note for the div in the page with the iframe position is absolute while in the single page relative.
First example embeds another page in it via iframe while the second example does the same in a single page.
Example 1
Mainpage
Code:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>Untitled</title>
</head>
<body>
<div style="position:absolute;top:100px;left:100px;">
<iframe src="./Page1.html" scrolling="No" frameborder="0" style="width: 548px; height: 150px"></iframe>
</div>
</body>
</html>
iframe for above
Code:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>MSDN Site Search via Google</title>
<style media="screen" type="text/css">
fieldset
{
border: 1px solid #781351;width: 20em;
padding-left: 21px;
padding-bottom: 1em;
width:348px;
position:relative;
background-color: #ffff00;
}
/* legend, postion and top are IE tweaks to ensure background does not bleed */
legend {position: relative;top:-0.75em;color: #fff;background: #ffa20c;border: 1px solid #781351;padding: 2px 6px; margin-bottom:15px}
input {color: #781351;background: #fee3ad;border: 1px solid #781351;margin-bottom:10px;}
.submit input {color: #000;background: #ffa20f;border: 2px outset #d7b9c9}
span {margin-bottom:10px;color: #DEB887;vertical-align: top;}
</style>
<script language="javascript" type="text/javascript">
function MSDN_Site_Search()
{
document.write("<a HREF='http://www.google.ca/search?as_q=" + document.mainForm.inputtext1.value + "&as_epq=&as_oq=&as_eq=&as_nlo=&as_nhi=&lr=&cr=&as_qdr=all&as_sitesearch=http%3A%2F%2Fmsdn.microsoft.com&as_occt=any&safe=active&tbs=&as_filetype=&as_rights=' title='Return to home page'>" + document.mainForm.inputtext1.value + "</a>");
}
</script>
</head>
<body>
<form name="mainForm">
<fieldset>
<legend>MSDN Search</legend>
<input type="text" id="inputtext1" value="VB.NET" style="width: 300px;" />
<input type="button" value="GO" style="width:332px" onClick="MSDN_Site_Search();" style="width: 400px;">
</fieldset>
</form>
</body>
</html>
Single page, does same as above
Code:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html>
<head>
<title>MSDN Site Search via Google</title>
<style media="screen" type="text/css">
fieldset
{
border: 1px solid #781351;width: 20em;
padding-left: 21px;
padding-bottom: 1em;
width:348px;
position:relative;
left:100px;
top:100px;
background-color: #ffff00;
}
/* legend, postion and top are IE tweaks to ensure background does not bleed */
legend {position: relative;top:-0.75em;color: #fff;background: #ffa20c;border: 1px solid #781351;padding: 2px 6px; margin-bottom:15px}
input {color: #781351;background: #fee3ad;border: 1px solid #781351;margin-bottom:10px;}
.submit input {color: #000;background: #ffa20f;border: 2px outset #d7b9c9}
span {margin-bottom:10px;color: #DEB887;vertical-align: top;}
</style>
<script language="javascript" type="text/javascript">
function MSDN_Site_Search()
{
document.write("<a HREF='http://www.google.ca/search?as_q=" + document.mainForm.inputtext1.value + "&as_epq=&as_oq=&as_eq=&as_nlo=&as_nhi=&lr=&cr=&as_qdr=all&as_sitesearch=http%3A%2F%2Fmsdn.microsoft.com&as_occt=any&safe=active&tbs=&as_filetype=&as_rights=' title='Return to home page'>" + document.mainForm.inputtext1.value + "</a>");
}
</script>
</head>
<body>
<form name="mainForm">
<fieldset>
<legend>MSDN Search</legend>
<input type="text" id="inputtext1" value="VB.NET" style="width: 300px;" />
<input type="button" value="GO" style="width:332px" onClick="MSDN_Site_Search();" style="width: 400px;">
</fieldset>
</form>
</body>
</html>