html,body,header,p,h1,div{
    padding: 0;
    margin: 0;
    font-family:Helvetica,Arial,sans-serif;
}
header{
    width: 100%;
    text-align: center;
}
header .head_box{
    width : 500px;
    margin: 10px auto;
    overflow: hidden;
}
header .head_box h1{
    margin: 20px;
    font-size: 50px;
    color: #333;
    font-weight: bold;
    float: left;
}
header .btn{
    width: 100px;
    margin: 20px auto 0;
    padding: 10px;
    background-color: #8f7a66;
    display: block;
    color: #ffffff;
    border-radius: 10px;
    text-decoration: none;
    float: right;
}
header .btn:hover{
    background-color: #9F8B77;
}
header .score{
    margin: 10px;
    font-size: 25px;
    clear: right;
    float: right;
}
.grid_container{
    width: 460px;
    height: 460px;
    padding: 20px;
    margin: 0 auto;
    background-color: #bbada0;
    border-radius: 10px;
    position: relative;
}
.grid_cell{
    width: 100px;
    height: 100px;
    border-radius: 6px;
    background-color: #ccc0b3;
    position: absolute;
}
.num_cell{
    border-radius: 6px;
    text-align: center;
    font-family: Helvetica, Arial,sans-serif;
    position: absolute;
}
footer{
    margin-top: 20px;
    color: #666;
    text-align: center;
}