Upscaling Images to Fit Bounding Boxes Using CSS-Only:

The challenge presented is to upscale an image to fit within a bounding box while preserving its aspect ratio. The provided CSS code handles downscaling but not upscaling.

CSS3 Solution:

Fortunately, CSS3 offers a solution:

.bounding-box {
  background-image: url(...);
  background-repeat: no-repeat;
  background-size: contain;
}

HTML Structure:

With this approach, the image is set as a background image of the bounding box element. The background-size: contain property ensures that the image scales to fill the bounding box without cropping or distorting it.

Compatibility:

This solution has good compatibility with modern browsers. For the latest compatibility information, refer to http://caniuse.com/background-img-opts.

Centering:

To center the image within the bounding box, the following variation can be used:

.bounding-box {
  background-image: url(...);
  background-size: contain;
  position: absolute;
  background-position: center;
  background-repeat: no-repeat;
  height: 100%;
  width: 100%;
}