Im trying to add themes but when im adding this under frontend=
javascript_version: latest
themes: !include themes.yaml
i get this fault = Error loading /config/configuration.yaml: ‘utf-8’ codec can’t decode byte 0xf6 in position 4851: invalid start byte
When i check config.
Where is your themes.yaml relative to your configuration.yaml, and what is the contents of it?
https://pastebin.com/e5zF9xMB thats what i have in themes.yaml and i have configuration and themes in same folder
Remove the capital letters from the start of the theme names and double check your indentation.
The issue is with the ö in Mörkt:
You either have to save it in utf-8 format or change the ö to an o or something else.
Thanks its working now 
had to change the ö.