Ask HN: How can I find out what libraries a website is using?

Often when browsing the internet I come across websites I find beautiful and there are certain elements I feel I could use in future. However sometimes I find it difficult to understand how a website has been made (what languages) and what libraries have been used for the frontend.

One particular site I have come across I am having trouble with is: http://yungcloud.com/

What can I do to try and discover more about how the website was made.