How to draw such a line, from one block to another?

Question

css

I don't understand how to draw such a line from one block to another

Answer 1

Something like this: https://jsfiddle.net/rockon404/p5x64477/
You can change the curvature of the line. Here is the rule:

height: $value1;  
border-radius: 50%/$value2 $value3 0 0;

$value2 and $value3 must be less than or equal to $value1