Basically, transferring the style content of one desired image to our input image is neural-style-transfer. Just like painting a Masterpiece but with CNN rather than a brush :)
started Reading about style transfer..from medium : https://medium.com/tensorflow/neural-style-transfer-creating-art-with-deep-learning-using-tf-keras-and-eager-execution-7d541ac31398
There is a paper written on neural style transfer by Leon A. Gatys :https://arxiv.org/pdf/1508.06576.pdf
Try to understand loss functions:-
1>content loss/
2>style loss/
*watch Andrew Ng lectures on style transfer*.
Understand why we are using middle layers and not the first and last layers.
select content and style layers.
Read about the dimesion flow of tensor...It will help you to write code.