Images and videos not resizing on mobile

[TechXero]

The problem is the plugin CSS file "mybbfancybox.css"

Edit this theme file on advanced mode and add at end:

@media only screen and (max-width: 680px) {
  .scaleimages img {
      max-width: 100%;
  }
}

Am a noob I have a temp admin account if you can help fix it