
Make It Disappear
<style type="text/css">
.subheading { display: none; }
</style>

Borders
Subheading actually refers to a row of a table, rather than the table itself. The table the subheading row
in, is called journalentry, but, just to confuse you, so is the main table each entry is in. Therefore to style
this inner journalentry table, we refer to
.journalentry .journalentry like this:
<style type="text/css">
.journalentry .journalentry { border: 1px solid red; }
</style>
[ More Border Styles ]

Background
To get rid of the existing background color:
<style type="text/css">
.subheading { background: transparent; }
</style>
Or to set a color of your own:
<style type="text/css">
.subheading { background: orange; }
</style>
Or a background image:
<style type="text/css">
.subheading { background: url('http://www.PATH TO YOUR IMAGE.gif'); }
</style>
More on
[ Backgrounds ]

Styling Text
<style type="text/css">
.subheading {
color: red;
font-family: "Times New Roman", Times, serif;
}
</style>
You can also style the date bit separately- to apply styles only to the date:
<style type="text/css">
.subheading small {
color: orange;
font-family: "Times New Roman", Times, serif;
}
</style>
More
[ Text Styles ]