html,body{
    width: 100%;
    height: 100%;
    overflow: hidden;
    background-color: #f5f5f5;
}
.circle{
    position: fixed;
    border-radius: 50%;
    text-align: center;
    color: white;
}
.anime1{
    animation: appear 0.5s linear forwards;
}
.anime2{
    animation: disappear 0.5s linear forwards;
}
.info{
    display: flex;
    flex-wrap: nowrap;
    justify-content: space-between;
    padding: 0 20px;
}
#score_box{
    font-size: 24px;
}
#time_box{
    font-size: 24px;
}
.cover{
    position: fixed;
    width: 100%;
    height: 100%;
    top: 0;
    left: 0;
    background-color: #f5f5f5;
    text-align: center;
    z-index: 10;
    padding: 100px 200px;
    box-sizing: border-box;
}
.game_info{
    font-size: 20px;
}
.btn_box{
    width: 200px;
    margin: 10px auto;
    display: flex;
    flex-direction: column;
    text-align: center;
}
.difficult{
    width: 120px;
    height: 40px;
    border: none;
    border-radius: 20px;
    background-color: #66ccff;
    color: white;
    font-size: 22px;
    margin: 10px auto;
    cursor: pointer;
}
.ready{
    width: 300px;
    height: 300px;
    position: fixed;
    left: calc(50% - 150px);
    top: calc(50% - 150px);
    background-color: #dddddd;
    color: white;
    font-size: 150px;
    font-family: "黑体";
    text-align: center;
    line-height: 300px;
    border-radius: 50%;
    z-index: 9;
}
.countdown{
    width: 300px;
    height: 300px;
    position: fixed;
    left: calc(50% - 150px);
    top: calc(50% - 150px);
    background-color: #dddddd;
    color: white;
    font-size: 250px;
    font-family: "黑体";
    text-align: center;
    line-height: 300px;
    border-radius: 50%;
}
.index1{
    z-index: 8;
}
.index2{
    z-index: 7;
}
.index3{
    z-index: 6;
}
.index4{
    font-size: 150px;
    z-index: 5;
}
@keyframes disappear {
    0%{
        transform: scale(1);
        opacity: 0.9;
    }
    10%{
        transform: scale(1.2);
        opacity: 0.9;
    }
    25%{
        transform: scale(1);
        opacity: 0.9;
    }
    60%{
        transform: scale(0.5);
        opacity: 0.6;
    }
    100%{
        transform: scale(0);
        opacity: 0;
    }
}
@keyframes appear {
    0%{
        transform: scale(0);
        opacity: 0;
    }
    40%{
        transform: scale(0.5);
        opacity: 0.6;
    }
    75%{
        transform: scale(1);
        opacity: 0.9;
    }
    90%{
        transform: scale(1.2);
        opacity: 0.9;
    }
    100%{
        transform: scale(1);
        opacity: 0.9;
    }
}