Why is there a pop-up window on page load?

Question

css

When loading a page, a pop-up window appears and disappears for a few seconds? In connection with what does it appear?

ilyin1ib.beget.tech

All code https://jsfiddle.net/8rwh5nvk/1/

Answer 1

.popup {
    position: fixed;
    width: 100%;
    height: 100%;
    top: 0;
    left: 0;
    bottom: 0;
    right: 0;
    background-color: rgba(0, 0, 0, 0.5);
    z-index: 1000;
    text-align: center;
    display: flex;
    justify-content: center;
    align-items: center;
}

Initially the window is visible, after the js is loaded, the closing is triggered
$('.popup').fadeOut();