#div_img {
    margin-left: 10px;
    width: 800px;
    height: 400px;
    border: 1px solid #000;
}

#pre_img {
    margin-top: 10px;
    margin-left: 10px;
    width: 600px;
    height: 200px;
    border: 1px solid #000;
}

h1 {
    margin-top: 10px;
    text-align: center;
}

img {
    width: 100%;
    height: 100%;
}

#tishi {
    color: blue;
}

#btn {
    margin-left: 10px;
    margin-bottom: 20px;
}

#putbtn {
    margin-left: 10px;
    margin-bottom: 10px;
}