Having Trouble Changing the Background to Black

Having Trouble Changing the Background to Black

I'm really new to Programming with Jquery Mobile and can't figure out how to change the background to black... I've done it before but for some reason I can't get it to change...

Here is what I'm working on... When you click on the Male or Female Button a male or female image appears, I want the background behind the image and the buttons to be black...
Also, is there a way to have the male image show before clicking a button?
Thanks for the Help you guys are awesome!
Here is the Code:
<!DOCTYPE html>
<html>
<head>
<title>jQuery Mobile Web App</title>
<link href="http://code.jquery.com/mobile/1.3.0/jquery.mobile-1.3.0.min.css" rel="stylesheet" type="text/css"/>
<script src="http://code.jquery.com/jquery-1.8.3.min.js" type="text/javascript"></script>
<script src="http://code.jquery.com/mobile/1.3.0/jquery.mobile-1.3.0.min.js" type="text/javascript"></script>





<div data-role="page" id="page">
<div data-role="header" data-theme="b">
<h1>VMT</h1>
</div>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title></title>





</script><script>
$(function(){
$('#image').hide();
$('#male').click(function(){
$("#male").attr('checked', true);
$("#female").attr('checked', false);
$('#image' ).html('<img src="MaleHF.jpg">');
$('#image').show();
});
$('#female').click(function(){
$("#female").attr('checked', true);
$("#male").attr('checked', false);
$('#image' ).html('<img src="FemaleHF.jpg">');
$('#image').show();
});
});
















</script>
<div data-role="fieldcontain">
<fieldset data-role="controlgroup" data-type="horizontal">
<form>
<div id="image"></div>
</form>
<label>
<input name="male" type="radio" id="male" value="male" data-theme="b">
Male</label>
<label>
<input name="female" type="radio" id="female" value="female" data-theme="b">
Female</label>









</body>
</html>