how to do this, coloring lines (like git)?
here is an example where it is used: 
CodePudding user response：
add the symbol and - (with diff syntax in markdown)
| symbol | |
- |
|---|---|---|
| name | Addition | Deletion |
| color | Green | Red |
| what it does do? | code that being added or changed code | code that being deleted or removed |
how to write it in MD?
```diff
-hello
hello world
```
how it will look?
real example to copy and paste.
```diff
-hello
hello world
```
see here, I created a gist for you: 
the first thing that came to my mind is the command diff, and I tried to search if diff is actually used in markdown, and it turns out that the info is true so it was real.
so use diff instead of javascript/python, or whatever...
https://gist.github.com/Laaouatni/1f0825dc0c531eb7cfb49ecc9560094c (click raw to copy code)
by using a
difflanguage name, now you can have this special design. also, this works only in GitHub, and you can't color highlight for a specified language like python or javascript for example... so use it when necessary to point a breaking change for example.