/* X-Small devices (portrait phones, less than 576px)
No media query for `xs` since this is the default in Bootstrap */
#desktop-image { display: none; }
#mobile-image { display: block; }

/* Small devices (landscape phones, 576px and up) */
@media (min-width: 576px) { 
  ...
}

/* Medium devices (tablets, 768px and up) */
@media (min-width: 768px) { 
  #desktop-image { display: block; }
  #mobile-image { display: none; }
}

/* Large devices (desktops, 992px and up) */
@media (min-width: 992px) { ... }

/* X-Large devices (large desktops, 1200px and up) */
@media (min-width: 1200px) { ... }

/* XX-Large devices (larger desktops, 1400px and up) */
@media (min-width: 1400px) { ... }