html, body {
    padding: 0;
    margin: 0;
    background: #e1ecfe;
    font-size: 14px;
}

#main_img {
    text-align: center;
}

@media only screen and (min-width: 720px) {
    #main_img #mobile {
        display: none;
    }

    #main_img #pc {
        width: 1600px;
    }
}

@media only screen and (max-width: 720px) {
    #main_img #mobile {
        max-width: 100%;
        display: block;
    }

    #main_img #pc {
        display: none;
    }
}