style.css

html {
    box-sizing: border-box;
    font-family: 'Permanent Marker';
    background-color: #606c38;
}

.header {
    text-align: center;
    font-size: 2vh;
}

.game-board-container {
    display: grid;
    grid-template-columns: 1fr 1fr 1fr;
    grid-template-rows: 1fr 1fr 1fr;
    width: 50vw;
    height: 50vw;
    margin: 40px auto 40px auto;
}

[class^="board-tile"] {
    display: flex;
    align-items: center;
    justify-content: center;
    width: calc(50vw / 3);
    height: calc(50vw / 3);

    font-size: calc(40vw / 3);
}

.board-tile-1, .board-tile-4, .board-tile-7 {
    border-right: 4px solid black;
    border-left: 4px solid black;
}

.board-tile-3, .board-tile-4, .board-tile-5 {
    border-top: 4px solid black;
    border-bottom: 4px solid black;
}

.turn-display {
    text-align: center;
    font-size: 2vh;
}

.new-game {
    text-align: center;
}

#restart-game-button {
    justify-content: center;
    align-items: center;
    color: #606c38;
    font-family: 'Permanent Marker';
    font-size: 25px;
    background-color: black;
    border-radius: 8px;
    height: 7vh;
    width: 30vw;
    border: 8px solid black;
}

#restart-game-button:hover {
    border: 8px solid black;
    border-radius: 8px;
    color: black;
    background-color: #606c38;
}