网站导航栏有下拉菜单，但是下拉菜单出现后会把下面的内容顶下去，这个怎么办？？？求大神

// 通过id获得节点

function $(id){

	return document.getElementById(id);

}



// 获取兄弟节点

function brothers(elem) {

	var r = [];

	var n = elem.parentNode.firstChild;

	for ( ; n; n = n.nextSibling ) {

	    if ( n.nodeType === 1 && n !== elem ) {

	        r.push( n );

	    }

	}

	return r;

}

//----------------------------------

//          导航栏

//----------------------------------



// 鼠标移动到导航栏上

function mouse_over_navbar(id) {



	// 获得菜单分类的下一个兄弟节点

	var child = brothers($(id));

	child[0].style.display = "block";

}



// 鼠标移开导航栏的下拉菜单

function mouse_out_navmenu(id) {

	// 获得菜单分类的下一个兄弟节点

	var child = brothers($(id));

	child[0].style.display = "none";

}



// 鼠标移开导航栏的下拉菜单

function get_menu_node(id) {

	// 获得菜单分类的下一个兄弟节点

	var child = brothers($(id));

	return child[0];

}



function hide_menu(which) {

	which.style.display = 'none';

}



// 获得导航栏下拉菜单

// 绑定事件

window.onload = function()

{

	// 导航栏有下拉列表的id值

	var navid1 = "navbar-intro";

	var navid2 = "navbar-organ";

	var navid3 = "navbar-teachers";

	var navid4 = "navbar-edu";

	



	// 绑定鼠标经过导航栏的事件

	$(navid1).onmouseover = function() {

		mouse_over_navbar(navid1);

	}

	$(navid2).onmouseover = function() {

		mouse_over_navbar(navid2);

	}

	$(navid3).onmouseover = function() {

		mouse_over_navbar(navid3);

	}

	$(navid4).onmouseover = function() {

		mouse_over_navbar(navid4);

	}

	

	

}

 

    

   

   



                    

                        


                            

                            

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