How is the shadow effect for objects made and are there similar libraries?

Question

css

Hello.
Here is an example of shadows:

How and with what to do this on a web page for all visual elements?
In advance, Thank you all for your help!

Answer 1

Make on svg, rect (colored square) and path (will act as a shadow). Depending on the position of the source, change the coordinates for path. 4x coordinates are enough, two near the square, two outside the container.