body {
    margin: 0;
    font-family: sans-serif;
}

#back {
    height: 100vh;
    width: 100vw;
    display: grid;
    place-content: center;
    place-items: center;
}

#message {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    font-size: 90px;
    font-weight: bold;
    pointer-events: none;
}

.hard {
    background-color: #ffb366;
    background-image:
        repeating-linear-gradient(-45deg, #fcc351, #fcc351 8px, transparent 0, transparent 16px);
}

.easy {
    background-color: #d1ff66;
    background-image:
        repeating-linear-gradient(-45deg, #c9fc51, #c9fc51 8px, transparent 0, transparent 16px);
}

h1 {
    font-size: 40px;
    font-weight: bold;
}

/* 3x3のマス目の配置を決めている */
#game {
    display: grid;
    grid-template-rows: repeat(3, 150px);
    grid-template-columns: repeat(3, 150px);
    grid-gap: 5px;
}

.cell {
    font-size: 130px;
    font-weight: bold;
    user-select: none;
    display: flex;
    align-items: center;
    justify-content: center;
    background-color: #ffffff55;
    backdrop-filter: blur(3px);
}

.o {
    color: #f48fb1;
}

.x {
    color: #2196f3;
}