background color in github readme markdown code example

Example 1: how to add color in text github readme

```diff
- text in red
+ text in green
! text in orange
# text in gray
@@ text in purple (and bold)@@
```

Example 2: change text color in md file

- ![#f03c15](https://via.placeholder.com/15/f03c15/000000?text=+) `#f03c15`
- ![#c5f015](https://via.placeholder.com/15/c5f015/000000?text=+) `#c5f015`
- ![#1589F0](https://via.placeholder.com/15/1589F0/000000?text=+) `#1589F0`