style.css

@import url("https://fonts.googleapis.com/css2?family=Fredoka+One&family=Rampart+One&display=swap");

html {
    height: 100%;
}

body {
    margin: 0;
    flex-direction: column;
    background-color: #fafafa;
    justify-content: center;
}

h1 {
    font-family: "Rampart One", cursive;
    font-size: 3.75em;
    letter-spacing: 15px;
    color: #535353;
    margin-bottom: 20px;
    text-align: center;
    user-select: none;
}

h2 {
    font-family: Verdana, Geneva, Tahoma, sans-serif;
    font-weight: bold;
    font-size: 30px;
    color: #4d4d4d;
    margin: 1em;
    letter-spacing: 1px;
    text-align: center;
    user-select: none;
}

a {
    color: #3d3e3c;
    font-family: 'Open Sans', sans-serif;
    font-size: 20px;
    margin: 0.5em 0;
    text-decoration: none;
    user-select: none;
    cursor: pointer;
}

a:hover {
    opacity: 0.8;
}

button:hover {
    opacity: 0.9;
}

.flex {
    display: flex;
    align-items: center;
}

#gameboard {
    background-color: #808080;
    border-radius: 10px;
    border: 5px solid #808080;
    display: grid;
    grid-template: repeat(3, 1fr) / repeat(3, 1fr);
    height: 400px;
    margin: 0 auto;
    width: 400px;
}

.cell {
    align-items: center;
    background-color: #d9d9d9;
    border-radius: 10px;
    border: 5px solid #808080;
    display: flex;
    font-family: "Fredoka One", cursive;
    font-size: 5em;
    font-weight: bold;
    justify-content: center;
    user-select: none;
    cursor: pointer;
}

.cell:hover {
    background-color: #e2e2e2;
}

#reset {
    font-family: Verdana, Geneva, Tahoma, sans-serif;
    font-size: 20px;
    margin: 25px;
    border: none;
    background-color: #5a9ec3;
    color: #fff;
    border-radius: 15px;
    height: 45px;
    width: 110px;
    font-family: "Fredoka One", cursive;
    letter-spacing: 2px;
    user-select: none;
    cursor: pointer;
}

#reset:hover {
    cursor: pointer;
}

.o {
    color: #64b0d9;
}

.x {
    color: #d92525;
}