<div margin: auto><style>
.search {
width: 800px;
float: left;
margin: 10%;
}
.searchform {
}
</style><div >
<form method="get" id="searchform" action="<?php bloginfo('home'); ?>/">
<input style="height: 30px; margin-right: 7px; width: 90%;" type="text" class="searchform" size="18" value="<?php echo wp_specialchars($s, 1); ?>" name="s" id="s" placeholder="Поиск по сайту" />
<input style="background-color: yellow; border: none; width: 80px; padding: 10px;color: red;" type="submit" id="searchsubmit" value="Поиск" class="btn" />
</form>
</div>