body {
    margin: 0;
    min-height: 100vh;

    display: flex;
    justify-content: center; /* 横中央 */
    align-items: center;     /* 縦中央 */
}

.logo-container img {
    max-width: 90vw;
    max-height: 90vh;
    width: min(80vw, 900px);
    height: auto;
    display: block;
}