Nothing tricky about toggling a search form, but making the search field focus upon showing was hard to find.
jQuery
jQuery(document).ready(function($) {
$(".search_icon").click(function() {
$(".evosearchform").slideToggle();
$("input:text:visible:first").focus();
});
$(document).keydown(function(e) {
if (e.keyCode == 27) {
$(".evosearchform").hide();
}
});
});
HTML
The toggle button (note .evosearch_icon displays a search icon as a bkgrd image):
<li class="search"><a class="search_icon"><span class="evosearch_icon"></span></a></li>
The search form (toggles open and closed)
<div style="display:none;" class="evosearchform">
<form method="get" id="search" action="<?php echo esc_url(home_url()); ?>">
<?php $req=''; ?>
<input type="text" autofocus name="s" id="s" placeholder="Search this site" value="<?php echo get_search_query(); ?>" />
<button type="submit">Search</button>
</form>
</div> 
