.scrollspy-example {
    position: relative;
    height: 30rem;
    margin-top: .5rem;
    overflow-y: scroll;
}
.card{
    max-width: 40rem;
}
.screen-hidden{
    max-width: 30rem;
}
@media (min-width: 0px) and (max-width: 768px) {
    .screen-hidden{
        display: none;
    }
    .logo{
        width: 10rem
    }
}
.biglogo{
    display: none;

    /* Location of the image */
    background-image: url('http://ai.ntu.edu.tw/wp-content/uploads/2019/07/bn-1500x430.jpg'); 
    min-height: 25rem;/*395.47px;*/
    /*min-width: 1378px; */
    background-size: contain;
    
    /* Image is centered vertically and horizontally at all times */
    background-position: center center;
    
    /* Image doesn't repeat */
    background-repeat: no-repeat;
    
    /* Makes the image fixed in the viewport so that it doesn't move when 
        the content height is greater than the image height */
    background-attachment: fixed;
    
    /* This is what makes the background image rescale based on its container's size */
    background-size: cover;
    
    /* Pick a solid background color that will be displayed while the background image is loading */
    background-color:#464646;
    
    /* SHORTHAND CSS NOTATION
        * background: url(background-photo.jpg) center center cover no-repeat fixed;
        */
}