style.css

header {
    display: block;
    width: 100%;
    margin: 0 auto;
    text-align: center;
}

header h1 {
    margin: 10px auto;
    font-family: Arial;
    font-size: 40px;
    font-weight: bold;
}

header #newgamebutton {
    display: block;

    width: 100px;
    margin: 10px auto;
    padding: 10px 10px;
    border-radius: 10px;

    background-color: #8f7a66;

    font-family: Arial;
    color: white;
    text-decoration: none;
}

header #newgamebutton:hover {
    background-color: #9f8b77;
}

header p {
    margin: 10px auto;

    font-family: Arial;
    font-size: 25px;
}

#grid-container {
    position: relative;

    width: 460px;
    height: 460px;
    margin: 50px auto;
    padding: 20px;
    border-radius: 10px;

    background-color: #bbada0;
}

.grid-cell {
    position: absolute;

    width: 100px;
    height: 100px;
    border-radius: 6px;
    background-color: #ccc0b3;
}

.number-cell {
    position: absolute;
    
    border-radius: 6px;
    font-family: Arial;
    font-size: 60px;
    font-weight: bold;
    line-height: 100px;
    text-align: center;
}