I found a way to style the Simple Opt-In module and thought it would be nice to share. Didn't see too many other posts about it.

Here's what I did with one simple mod to _OptInSimple.ascx

1.) In first table tag add a new class, I've called "tblSimpleOpt-In"

class="tblSimpleOpt-In"

2.) In Admin>Site Settings>StyleSheet, add the following to the portal stylesheet, I put mine at bottom.

/* =================================================== */
/* Custom styles for Simple Opt-In. (Requires mod to _OptInSimple.ascx) */
/* =================================================== */

/* whole table for Simple Opt-In */
.tblSimpleOpt-In {
    width:100%;
    }

/* Email address styles */
.tblSimpleOpt-In td {
   width:100%;
   font-size:12px;
   color: red;
   text-align:center;
   font-weight:bold;
   }

/* Subscribe link styles */
.tblSimpleOpt-In td a:link {
   color:red;
   font-size:12px;
   font-weight:bold;
   }

/* removes help icon */
.tblSimpleOpt-In td a img {
   display:none;
   }

This will give you some control over centering, font size and color, and removes the help icon.

Cheers!

Kelly