javascript问题

window.onload = function () {
            var lis = document.getElementsByTagName("li");
            var pics = document.getElementsByClassName("pic");
        

            for (var i=0; i<lis.length; i++){
                
                (function (i) {
                    lis[i].onmouseover = function(){
                        pics.style.visibility = "visible";
                    }
                })(i);
                
            }
        }

为什么不能修改 style不能这么用？

document.getElementsByClassName("pic");这获取的也是个数组 数组哪有.style
pics[i]