They basically used a form like this:
CODE
<form method="get" action="http://detuned.givemeenvy.org/previewer/index.php?layout=" name="css">
<select name="layout" onChange="document.css.submit();"><option value="">Select</option>
<option value=""></option>
<option value="boys_will_be_boys">boys will be boys</option>
<option value="faux_affliction">faux affliction</option>
<option value="if_you_swear_to_listen">if you swear to listen</option>
<option value="the_sour_and_the_sweet">the sour and the sweet</option>
<option value="time_square_cant_shine">time square cant shine</option>
<option value="trophy_boys_trophy_wives">trophy boys trophy wives</option>
<option value="wet_dream_for_the_webzine">wet dream for the webzine</option>
<option value="writing_you_a_symphony_of_sound">writing you a symphony of sound</option>
</select>
</form>
And it has the names of the layouts in the option value. But the name of the layout is case sensitive when typed in the value field.