Style transfer is the technique of recomposing images in the style of other images. Leon A. Gatys et al. who plublished "A Neural Algorithm of Artistic Style in 2015" proposed style transfer as an optimization problem which can be solved through training a neural network. The tutorial for developing the intuition of neural style transfer along with the implemented code can be found in style-transfer.ipynb.
Deep Dream uses neural style transfer and its implementation can be found in DeepDream.ipynb.
HTML versions of the ipynbs can be found at