Here's a hack to adjust the CSS styles for the autmatically-generated text input field and button. If you have something like this:
<!** Search index.tpl Search>
<!** Edit Search keywords>
<!** EndSearch>
Then you can do this to adjust the styles:
<script>
// For the text field
document.forms.search.SearchKeywords.style.border = "1px solid black";
document.forms.search.SearchKeywords.style.font = "8pt Verdana";
// For the button
document.forms.search.search.style.border = "1px solid black";
document.forms.search.search.style.font = "bold 8pt Verdana";
</script>