I've made a simple Handbook of custom CSS snippets to make the use of custom CSS simpler for non-developers.
All you have to do is find your required CSS code from the handbook and paste them in the Custom CSS section in your survey's design page.
Also, please let me know if want any CSS to be added to the list. I'll update them as well!
Link to Custom CSS Handbook: https://css.surveysparrow.com/