#loading {
    position: fixed; /* sayfanın scrolluna bağlı kalmaz */
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: 9999999;

    display: flex; /* flex kullan */
    align-items: center; /* dikey ortala */
    justify-content: center; /* yatay ortala */
}