The textarea is in html styled as font-family: monospace;
If I wanna have consistent appearance I apply this also for my text inputs.
For me it looks like good. But the question if it's "correct"?
Cause on the web it's usual to use for presentation (= what is on the screen style) some sans-serif font.
This monospace actualy have these little ends of letter similar to serif, which is better for printing (=>beter on paper).
So back to my question: Is the use monospace in this case in accordance with the customs of the Web or is it a mistake? I mean something that is good in this case to use?
"Good" is whatever you want it to be. Think about two things:
There is no right or wrong answer - except "it depends".