img.bg {
    margin-left: auto;
    margin-right: auto;
    /* Set rules to fill background */
    min-height: 100%;
    min-width: 100%;
    /* Set up proportionate scaling */
    width: 100%;
    height: auto;
    /* Set up positioning */
    position: absolute;
    top: 10px;
    left: 10px;
}