Oh ye of little faith. It's actually pretty easy to do.
If you're using a version you found online they're probably using the gram matrix approach from arxiv.org/pdf/1508.06576.pdf. I've been dissatisfied with that approach because images that look really different can appear identical by that metric. I'm experimenting with a variant based a Wasserstein metric instead. I think it gives superior results.
Looks interesting kinda, but yeah a bit repetitive
Ryan Fisher
Humans tend to show less expected results
Hudson Lewis
The details transferred depend on the textures of the style you imprint. The challenge is more transferring definitive style while still maintaining the structure of the image. Pic related is what happens with the old approach. It's hard to get a lot of style without washing out the image.