style.css

* {
    box-sizing: border-box;
    margin: 0px;
    padding: 0px;
}

body{
    background-color: #222831;
    color:#eeeeee;
}

h1{
    margin:10px;
}

ol{
    margin-left: 20px;
}

li{
    width: 100%;
    padding:5px;
    border:1px solid #6a727e;
}

.main{
    max-width: 700px;
    margin:2em auto;
    border:1px solid #ffd369;
    padding:5px;
    display:flex;
    overflow: hidden;
}

.game-section{
    width:50%;
}

.score-section{
    width:50%;
}

h2{
    width:100%;
    margin:10px;
    text-align: center;
}

table{
    border: none;
    margin:10px;
    border-collapse: collapse;
}

.btns{
    margin:10px;
}

td {
    width:100px;
    height:100px;
    border:1px solid #6a727e;
    font-size: 80px;
    text-align: center;
    padding:5px;
    cursor:pointer;
    display: inline-block;
    color:#eeeeee;
}

input{
    padding:5px;
    font-size: 20px;
    background:none;
    cursor:pointer;
    border:none;
}

.st-btn{
    background:rgb(81, 230, 81);
    color:white;
}

.rst-btn{
    background:rgb(114, 211, 250);
    color:white; 
}

@media screen and (max-width:630px){
    body{
        padding:5px;
    }

    .main{
        flex-direction: column;
        justify-content: center;
        align-items: center;
    }
    
    .game-section{
        width:100%;
        display: flex;
        flex-direction: column;
        justify-content: center;
        align-items: center;
    }

    .score-section{
        width:100%;
        display:flex;
        flex-direction: column;
        justify-content: center;
        align-items: center;
    }

    ol{
        width:100%;
    }
    
    li{
        width:100%;
        font-size: 20px;
        margin-left:5px;
    }
}