body {
    display: flex;
    justify-content: center;
    align-items: center;
}
.grid {
    display: grid;
    gap: 1px;
}
.cell {
    width: 50px;
    height: 50px;
    background-color: white;
    border: 1px solid black;
}
.btn {
    padding: 10px 20px;
    font-size: 16px;
    background-color: #55dd5c;
    color: #fff;
    border: none;
    cursor: pointer;
    position: absolute;
    bottom: 40px; /* 从页面底部向上偏移40px */
    margin-left: 10px;
}