style.css

*{
    margin: 0;
    padding: 0;
}

body {
    font-family: Arial, Helvetica, sans-serif;
    background: #83a4d4;
    background: linear-gradient(to right, #cff0f2, #95b0d7); 
}

table, tr, td {
    border: 4px solid black;
    padding: 6px 8px;
    border-collapse: collapse;
}

.main{
    display: flex;
    align-items: center;
    justify-content: center;
} 

.rules{
    max-width: 30%;
    margin: 2em 10em 0em 2em;
}

.rules ul li{
    font-size: 1.2em;
}

.game_board{
    max-width: 70%;
    margin: 2em 10em 0em 2em;
}

header{
    margin-top: 20px;
}

h1, h2 ,h3 {
    text-align: center;
    font-size: 2em;
    margin-bottom: 10px;
}

img {
    border-radius: 4px;
}

.btn{
    display: flex;
    align-items: center;
    justify-content: center;
}

.buttons
{
    margin-left: 0.8em;
    padding: 0.2em;
    width: 120px;
    height: 50px;
    background-color: #3897f0;
    border-radius: 30px;
    box-shadow: 9px 9px 12px #242425, -9px -9px 12px #a1a1a1;
    color: #fff;
    cursor: pointer;
    font-weight: bolder; 
    font-size: 14px;
    text-transform: capitalize;
    text-align: center;
    border: none;
    cursor: pointer;
}

.buttons:hover
{
    box-shadow: inset 4px 4px 6px #cccccc, inset -3px -3px 6px #a1a1a1; 
}