@media all and (min-width: 1001px) {
    .mainImageFon {
        position: relative;
        background: #fff url(loading.gif) no-repeat 50% 50%;
        margin-bottom: 10px;
    }

    .mainImageFon img {
        left: 0px;
        max-width: 100%;
        width: auto;
        right: 0px;
        margin-top: -100px;
    }
}

@media all and (max-width: 1000px) {
    .mainImageFon {
        position: relative;
        background: #fff url(loading.gif) no-repeat 50% 50%;
        margin-bottom: 10px;
        width: 100vw;
        left: calc(-50vw + 50%);
        margin-top: -40px;
    }

    .mainImageFon img {
        left: 0px;
        max-width: 100%;
        width: auto;
        right: 0px;
    }
}