I haven't done this, but I presume str_repeat is run on the category level.

You are right, Klas. I just don't know how to set the function str_repeat

Add category level field to the list or item, put php string typography on it and select str_repeat. Then you just need to add - or any other sign as string that will get repeated.

All this was made by me before you ask a question. And it's not working

I tried to reproduce the look from demo and this is working for me:

Put Category Level field in the Hidden position. Put php_string typography on it and enter — as character.

Put HTML typography on the Category title and insert this as html:

|$cck->getTypo('cat_level'); *value*