body {
    margin: 0;
    padding: 0;
    background-color: #cecfc8;
}
.mainImg {
    margin: 0 auto;
}
.mainImg img {
    display: block;
    margin-left: auto;
    margin-right: auto;
    height: 100%;
    max-width: 100vw;
    max-height: 100vh;
}