Wordpress Default Search Form
<?php
$searchVal = '';
if(isset($_GET['s'])){ $searchVal = $_GET['s']; }
?>
<form id="search-form" method="GET" action="<?php bloginfo('url'); ?>">
<input type="search" name="s" value="<?php echo $searchVal; ?>" placeholder="Search" maxlength="50" required="required">
<input type="submit" value="Go">
<input type="hidden" name="post_type" value="post">
</form>