我已经看了很多jquery示例，介绍了如何使菜单具有粘性。我已经在干净的html页面上应用了这些教程，它们非常有效。然而，当我尝试将其应用于“212”主题时，什么都没有发生。固定属性不会添加到menu类中。

这是CSS：

.sticky {
position: fixed;
width: 100%;
left: 0;
top: 0;
z-index: 100;
border-top: 0;
}

<nav id="site-navigation" class="main-navigation" role="navigation">
        <h3 class="menu-toggle"><?php _e( \'Menu\', \'twentytwelve\' ); ?></h3>
        <a class="assistive-text" href="#content" title="<?php esc_attr_e( \'Skip to content\', \'twentytwelve\' ); ?>"><?php _e( \'Skip to content\', \'twentytwelve\' ); ?></a>
        <?php wp_nav_menu( array( \'theme_location\' => \'primary\', \'menu_class\' => \'nav-menu\' ) ); ?>
</nav><!-- #site-navigation -->

$(document).ready(function() {
var stickyNavTop = $(\'.main-navigation\').offset().top;

var stickyNav = function(){
var scrollTop = $(window).scrollTop();

if (scrollTop > stickyNavTop) { 
    $(\'.main-navigation\').addClass(\'sticky\');
} else {
    $(\'.main-navigation\').removeClass(\'sticky\'); 
}
};

stickyNav();

$(window).scroll(function() {
    stickyNav();
});
});