.Miloader {
    position: fixed;
    left: 0px;
    top: 0px;
    width: 100%;
    height: 100%;
    z-index: 9999;
    background-color: rgba(249, 249, 249, 0.8);
    display: none;
}

.imgloader {
    background: url(../img/loader.svg) no-repeat;
    position: fixed;
    left: 50%; /* Centrado */
    top: 50%;
    transform: translate(-50%, -50%); /* Truco para centrar */
    width: 15%;
    height: 30%;
}

@media (max-width: 900px) {

    .imgloader {
        background: url(../img/loader.svg) no-repeat;
        position: fixed;
        left: 50%;
        top: 50%;
        transform: translate(-50%, -50%);
        width: 25%;
        height: 15%;
    }
}