.content{
    width:640px;
    height:640px;
    margin:100px auto;
    position:relative;
}
.btn{
    width:100%;
    height:100%;
    position:absolute;
    left:0px;
    top:0px;
    background-color:rgba(0,0,0,0.3);
    z-index:2;
}
.btn button{
    background-color: none;
    border:none;
    outline:none;
    background-size:100% 100%;
    cursor:pointer;
    position:absolute;
    left:50%;
    top:50%;
}
.start button{
    width:200px;
    height:80px;
    background-image:url(start.jpeg);
    margin-left:-100px;
    margin-top:-40px;
}
.pouse{
    display:none;
}
.pouse button{
    width:70px;
    height:70px;
    background-image:url(zanting.jpeg);
    margin-left:-35px;
    margin-top:-35px;
}
/* snake */
#snakewrapper{
    position: relative;
    width:600px;
    height:600px;
    background-color:#225676;
    border:20px solid #7dd9ff;
}

.snakehead{
    background-image:url(tanchishe.jpeg);
    background-size:cover;
}
.snakebody{
    background-color:#9ddbb1;
    border-radius:50%;
}
.snakefood{
    background-image:url(xiaopingguo.jpeg);
    background-size:cover;
}