
Make It Disappear
I'm going to skip this one, as I can't think of any circumstance under which you'd need it.

Borders
To get rid of the borders
<style type="text/css">
.comment_input, .comment_input td { border: none; }
</style>
To put a border of your own around it:
<style type="text/css">
.comment_input { border: 1px solid red; }
.comment_input td { border: none; }
</style>
[ More Border Styles ]

Background
To set a background color:
<style type="text/css">
.comment_input { background: red; }
</style>
Or a background image:
<style type="text/css">
.comment_input { background: url('http://www.PATH TO YOUR IMAGE.gif'); }
</style>
More on
[ Backgrounds ]

Styling Text
The comment_input table contains both plain text and links. You can style the text, links, and even links in
their hover state all separately:
<style type="text/css">
.comment_input {
color: red;
font-family: "Times New Roman", Times, serif;
}
.comment_input a:link, .comment_input a:visited {
color: orange;
font-size: 8pt;
text-decoration: none;
}
.comment_input a:hover {
color: green;
background: yellow;
font-size: 8pt;
text-decoration: underline overline;
}
</style>
More
[ Text Styles ]

Size
You can change the width of the comment input table:
<style type="text/css">
.comment_input { width: 400px; }
</style>

Positioning
You can use margins to set a bit more space to the top or bottom, or left or right of the comment_input table:
<style type="text/css">
.comment_input {
width: 400px;
margin-left: 200px;
margin-bottom: 60px;
}
</style>

Textarea, Subject & Button
To change the look and style of the textarea subject line & button:
<style type="text/css">
.comment_input input, .comment_input textarea {
background: yellow;
color: green;
font-size: 8pt;
border: 1px solid deeppink;
}
</style>