.Box:hover .btn{opacity: 1;}

.front {left: 0px;}
.back {left: 600px;}
.active {left: 300px; transform: scale(1.5); z-index: 10;}

.btns .btn {width: 60px; height: 60px; display: block; position: absolute; background-color: rgba(0,.5); font-size: 50px; font-family: "微软雅黑"; color:rgba(255,255,.5); line-height: 55px; text-align: center; cursor: pointer; z-index: 100; opacity: 0; transition:opacity .3s linear;}
.btns .btn:first-child {top: 125px;}
.btns .btn:last-child {top: 125px; right: 0px;}

var index = 2,front = 0,back = 0,offset = false,timer = setInterval(timer,5000);

for(var i=0;i<btns.length;i++){
(function(i){
btns[i].onclick = function(){click(i)};
})(i);

btns[i].onmouSEOver = function(){
offset = true;
}
btns[i].onmouSEOut = function(){
offset = false;
}
}

for(var i=0;i<imgs.length;i++){
imgs[i].onmouSEOver = function(){
offset = true;
}
imgs[i].onmouSEOut = function(){
offset = false;
}
}

function timer(){
console.log(offset)
if(offset){
return;
}
else{
click(1)
}
}

function click(x){
imgs[index].setAttribute('class','');
if(x === 0){
if(--index < 0){
index = --imgs.length;
}
front = back = index;
if(++front > --imgs.length){front = 0}
if(--back < 0){back = --imgs.length}
imgs[front].style.zIndex = '1';
imgs[back].style.zIndex = '0';
}
else{
if(++index > --imgs.length){
index = 0;
}
front = back = index;
if(++front > --imgs.length){front = 0}
if(--back < 0){back = --imgs.length}
imgs[front].style.zIndex = '0';
imgs[back].style.zIndex = '1';
}
imgs[index].style.zIndex = '10';
imgs[front].setAttribute('class','front')
imgs[back].setAttribute('class','back')
imgs[index].setAttribute('class','active');
}
}