depends where you want to add button in the form or out?
goo to /templates/base/scripts/BxBaseFunction.php about line 557
for exemple i have edit my search form:
<div id="sys_search_wrapper">
<div id="sys_search" class="bx-def-margin-left">
<form class="ajax_form" action="searchKeyword.php" method="get" name="SearchForm">
<input type="text" name="keyword" id="keyword" value="<?= $sSearchC ?>" class="top_search bx-def-font" />
<input class="top_submit" type="submit" alt="Search" name="" value="" />
</form>
</div>
</div>
<div class="clear_both"></div>
you ned to add new class in css and edit this class as your needs:
form.ajax_form {
background-color: #FFFFFF;
border-color: #666666 #DDDDDD #DDDDDD #666666;
border-radius: 3px 3px 3px 3px;
border-style: solid;
border-width: 1px;
height: 30px;
margin-left: 0;
position: relative;
width: 500px;
}
.top_search {
background: none repeat scroll 0 0 transparent;
border: 0 none;
color: #999999;
margin-left: 1px;
margin-top: 1px;
padding: 7px 0 7px 4px;
width: 465px;
}
input.top_submit[type="submit"] {
background: url("../images/your_buton.png") no-repeat scroll center top transparent;
border: medium none;
cursor: pointer;
height: 20px;
margin: 6px;
outline: medium none;
padding: 0;
position: absolute;
width: 15px;
}
if you ned more help seend me PM