Flip / mirror an image horizontally + vertically with css

Try this:

.img-hor-vert {
    -moz-transform: scale(-1, -1);
    -o-transform: scale(-1, -1);
    -webkit-transform: scale(-1, -1);
    transform: scale(-1, -1);
}

Updated fiddle: https://jsfiddle.net/7vg2tn83/1/

It wasn't working before because you were overriding the transform in your css. So instead of doing both, it just did the last one. Sort of like if you did background-color twice, it would override the first one.

To perform a reflection you can use, the transform CSS property along with the rotate() CSS function in this format:

transform: rotateX() rotateY();

The function rotateX() will rotate an element along the x-axis and the function rotateY() will rotate an element along the y-axis. I find my approach intuitive in that one can visualize the rotation mentally. In your example, the solution using my approach would be:

.img-hor {
  transform: rotateY(180deg); // Rotate 180 degrees along the y-axis
}

.img-vert {
  transform: rotateX(180deg); // Rotate 180 degrees along the x-axis
}

.img-hor-vert {
  transform: rotateX(180deg) rotateY(180deg); // Rotate 180 degrees on both
}

The JS fiddle to demonstrate the solution is https://jsfiddle.net/n20196us/1/