Theme dropdown select form element

Here's the larger outtake from the ADT stylesheet Agaric looked at:

/* form elements */
form {
/*ADT*/margin:5px; padding: 5px;
border: 1px solid #f2f2f2;
background-color: #FAFAFA;
}
label {
display:block;
font-weight:bold;
margin:5px 0;
}
input {
padding: 2px;
border:1px solid #eee;
font: normal 1em "Trebuchet MS", Tahoma, sans-serif;
color:#777;
}
select {
padding: 1px;
border:1px solid #eee;
font: normal 1em "Trebuchet MS", Tahoma, sans-serif;
color:#777;
}
textarea {
width:400px;
padding:2px;
font: normal 1em "Trebuchet MS", Tahoma, sans-serif;
border:1px solid #eee;
height:100px;
display:block;
color:#777;
}
form input.form-submit {
margin: 0;
font: bold 1em Arial, Sans-serif;
background: #FFF url(images/gradientbg.jpg) repeat-x;
padding: 2px 0px!important;
color: #333;
border: 1px solid #DADADA;
}

/* search form */
/***ADT***/
.block-search {
background-color: transparent;
border: none;margin: 0; padding: 0;
}
.block-search input.form-text {
width: 130px;
color: #333;
height: 20px;
padding: 2px;
vertical-align: top;
}

.block-search input.form-submit {
font: bold 12px Arial, Sans-serif;
color: #333;
width: 60px;
height: 26px;
border: 1px solid #DADADA;
padding: 3px 5px;
vertical-align: top;
}

#sidebar .block-search div.content {
margin:0;
padding:0;
}

form#search-block-form {
background:none;
border:none;
width:auto;
margin:0;
padding:0;
/* Drupal core css has too much styling!... */
}

/*** ADT Theme Switcher ***/

.block-switchtheme form select {
width:120px;
margin-right:5px;
}

And the form element it applied to on their site:

<div id="block-switchtheme-0" class="block block-switchtheme">

<h2>Theme</h2>

<div class="content"><form action="/preview/node/2" method="post" id="switchtheme-switch-form">
<div><div class="form-item">
<select name="custom_theme" title="Change the way this site looks." class="form-select" id="edit-custom-theme" ><option value="adt_bluebusiness">adt_bluebusiness</option><option value="adt_bluepigment">adt_bluepigment</option><option value="adt_envision">adt_envision</option><option value="adt_higherground">adt_higherground</option><option value="adt_pixelgreen" selected="selected">adt_pixelgreen</option><option value="bluemarine">bluemarine</option><option value="garland">garland</option></select>
</div>
<input type="submit" name="op" id="edit-submit" value="Switch" class="form-submit" />
<input type="hidden" name="form_id" id="edit-switchtheme-switch-form" value="switchtheme_switch_form" />

</div></form>
</div>