Compare images page alignment

I would like the image to be aligned in the middle (horizontally) of the page. How can I fix this?
https:// xerte.deltion.nl/play.php?template_id=10519#afbeelding-vergelijker

Change the slider position optional property?

My question concerns the margins on the left and right side of the image. There is significantly less space on the left than on the right. I would like the space on both sides to be equal so that the image is nicely centered.

Try
.holder {
position: initial;
}

Much better. Thank you!