$(function(){
    // 屏幕滚动
    $(window).scroll(function (){
        var str = $(this).scrollTop();
        navigation(str);
    });

    
})

 /*
 *   获取 DOC 超出可视区域的高度
 */
 var dir = $(document).scrollTop();  
 navigation(dir);

function navigation(st){
    if(st >180){
        $('.m_top').css('background','rgba(255,255,255,1)');
        $('.m_top a.m_be').find('img').attr('src','/image/back_1.png');
        $('.m_top a.menu').find('img').attr('src','/image/menu_a_1.png');
        $('.m_top .m_title').show();
    }else if(st>80 && st <= 180){
        $('.m_top a.m_be').find('img').attr('src','/image/back_1.png');
        $('.m_top a.menu').find('img').attr('src','/image/menu_a_1.png');
        $('.m_top').css('background','rgba(255,255,255,0.8)');
        $('.m_top .m_title').show();
    }else{
        $('.m_top').css('background','rgba(255,255,255,0)');
        $('.m_top a.m_be').find('img').attr('src','/image/lp_index/back.png');
        $('.m_top a.menu').find('img').attr('src','/image/index/menu_a.png');
        $('.m_top .m_title').hide();
    }
    // 显示 与 隐藏 二级导航
    if(st > 180){
        $('.w_find_nav').fadeIn();
    }else{
        $('.w_find_nav').fadeOut();
    }
}