styles.css

*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    font-family: 'Poppins', 'sans-serif';
}

.wrapper {
    width: 100vw;
    height: 100vh;
    background-image: url(./assets/gradient-bg.jpg);
    background-size: cover;
    background-position: center;
    display: grid;
    place-items: center;
}

.game-info {
    color: white;
    position: absolute;
    top: 3rem;
    left: 50%;
    transform: translateX(-50%);
    background-color: rgba(255, 255, 255, 0.15);
    backdrop-filter: blur(7px);
    border-radius: 1rem;
    border: 1px solid rgba(255, 255, 255, 0.25);
    padding: 0.5rem 3rem;
    text-align: center;
    box-shadow: 0 4px 10px rgba(0, 0, 0, 0.3);
}

.tic-tac-toe {
    width: 90%;
    max-width: 20rem;
    background-color: rgba(255, 255, 255, 0.15);
    backdrop-filter: blur(7px);
    border-radius: 1rem;
    border: 1px solid rgba(255, 255, 255, 0.25);
    padding: 2rem;
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    aspect-ratio: 1/1;
}

.box {
    position: relative;
    width: 100%;
    aspect-ratio: 1/1;
    cursor: pointer;
    font-size: 3rem;
    color: #f8f8f8;
    display: flex;
    justify-content: center;
    align-items: center;
    transition: all 150ms ease-in-out;
}

.box:hover {
    background-color: rgba(255, 255, 255, 0.05);
    transform: scale(1.05);
}

.box1, .box2, .box4, .box5 {
    border-right: 2px solid white;
    border-bottom: 2px solid white;
}

.box3, .box6 {
    border-bottom: 2px solid white;
}

.box7, .box8 {
    border-right: 2px solid white;
}

.btn {
    color: white;
    position: absolute;
    bottom: 3rem;
    left: 50%;
    transform: translateX(-50%);
    background-color: rgba(255, 255, 255, 0.15);
    backdrop-filter: blur(7px);
    border-radius: 1rem;
    border: 1px solid rgba(255, 255, 255, 0.25);
    padding: 0.5rem 2rem;
    cursor: pointer;
    transition: all 150ms ease-in-out;
    display: none;
}

.btn.active {
    display: flex;
    opacity: 0;
    animation: fadeIn 1s forwards;
    box-shadow: 0 4px 10px rgba(0, 0, 0, 0.3);
}

@keyframes fadeIn {
    to {
        opacity: 1;
    }
}

.win {
    background-color: rgba(0, 255, 0, 0.3);
    animation: glow 0.7s infinite alternate;
}

@keyframes glow {
    from {
        box-shadow: 0 0 10px rgba(0, 255, 0, 0.5);
    }
    to {
        box-shadow: 0 0 20px rgba(0, 255, 0, 1);
    }
}