Hi Oliinyk,
Have you tried with your theme’s documentation page?
Here’s the link:
https://demo.alxmedia.se/wp-content/themes/hueman/functions/documentation/documentation.html
This theme has a good number of style settings that you can easily adjust in the Theme Options panel.
If what you want to change can’t be done from there, then your best bet is to download the sample child theme from the documentation page and add your own css styles there.
I hope this helps.
Cheers ??
– Maria Antonietta.