How to post text with whitespaces ?

What do you mean whitespaces? Do you want some blank space after each post?

yes. But within a post, for text indention.

This help ?
https://elasticdog.com/2004/09/code-viewer/

If it’s just for the very occasional use, just use  

Or otherwise if you have the part that you wanted intended just style it using padding: top right bottom left;

It’s much more then I expected. Really great
Thanks a lot !!
Norbert