body {
    height: 100%;
    min-height: 100dvh;
}

.wrapper {
    min-height: 100dvh;
    opacity: 0;
    transition: opacity 1s ease-out;
}

.wrapper.show {
    opacity: 1;
}

.kv {
    width: 100%;
    height: 100dvh;

    position: absolute;
    left: 0;
    top: 0;
}

.canvasarea {
    width: 100%;
    height: 100%;
    /* 必要に応じて position: absolute; left: 0; top: 0; など */
}