style.css

html {
    font-family: sans-serif;
}

h1 {
    text-align: center;
    margin-top: 20px;
    margin-bottom: 100px;
}

#score-1, #score-2 {
    color: #000;
    font-size: 30px;
}

.scoreboard {
    width: 800px;
    height: 80px;
    margin-left: auto;
    margin-right: auto;
}

.player {
    color: gray;
    font-size: 20px;
}

.tic-tac-toe {
    margin-right: auto;
    margin-left: auto;
    margin-top: 20px;
    width: 600px;
    cursor: pointer;
}

.tic-tac-toe td {
    width: 150px;
    height: 150px;
    text-align: center;
    vertical-align: center;
}

table {
    border-collapse: collapse;
}
table td, table th {
    border: 1px solid black;
}
table tr:first-child td {
    border-top: 0;
}
table tr:last-child td {
    border-bottom: 0;
}
table tr td:first-child,
table tr th:first-child {
    border-left: 0;
}
table tr td:last-child,
table tr th:last-child {
    border-right: 0;
}